TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The preparation method of (I) comprises reacting molten 2-chloro-5-trichloromethyl pyridine (II) and catalyst with hydrogen fluoride in a closed system under anhydrous condition to obtain 2-chloro-5-trifluoro-methyl pyridine (I), where the mass ratio of the catalyst is 0.1-10%, preferably 0.1-2% the weight of (II), the molar ratio of hydrogen fluoride to (II) is 3:1-15:1, preferably 3:1-5:1, reaction temperature is 150-250 degrees C, preferably 160-210 degrees C, and reaction pressure is 2-10MPa, preferably 4-6MPa. The preparation of (II) comprises reacting 2-chloro-5-methyl pyridine (III) with chlorine gas in presence of light and/or initiator out with or without solvent to obtain (II), where (III) and initiator solution is reacted with chlorine gas at 30-180 degrees C, or initiator is added to (III) solution and then reacted with chlorine gas at 30-180 degrees C. The preparation of (III) comprises reacting (4E)-3-benzylhex-4-en-2-one compounds of formula (IV) with chlorinating reagent and N,N-disubstituted formamide in a solvent to obtain (III), where the chlorinating reagent solution is cooled to 0-20 degrees C, N,N-disubstituted formamide and (IV) are added dropwisely, and heating is performed at 70-120 degrees C to obtain (III). The preparation method (III) further comprises adjusting pH value to 9-11 by using alkali and distilling to obtain chloromethyl benzene compounds of formula (V). The preparation method of (IV) comprises (a) reacting phenylmethanamine compounds of formula (VI) with propionaldehyde to obtain reaction liquid, then mixing the obtained reaction liquid with inorganic strong alkali and separating, and (b) without post processing the liquid obtained in step (a) to obtain organic phase, then carrying out acetylation reaction with acetylation reagent in presence of organic alkali to obtain (IV), where (a) (VI) is cooled to 0-5 degrees C, propionaldehyde is added dropwise and reacting to obtain reaction solution, and then the reaction solution is mixed with inorganic strong alkali and separating, and (b) without processed organic phase is mixed with organic strong alkali, then cooling to 0-10 degrees C, and acetylating with acetylation reagent, or (a) (VI) is reacted with propionaldehyde at -20 to 20 degrees C for 0.5-5 hours, preferably 0-20 degrees C for 0.5-2 hours, the inorganic alkali is sodium hydroxide and/or potassium hydroxide, and the mass ratio of inorganic alkali to (VI) is 0.04-0.5, preferably 0.04-0.3, and (b) the organic alkali is organic amine, the molar ratio of organic amine to (VI) is 2-10, preferably 2-5, the acetylating reagent is acetyl chloride and/or acetic anhydride, the molar ratio of acetylating agent to (VI) is 1:1-3:1, preferably 1:1-1.5:1, and acetylation reaction temperature is 20-50 degrees C, preferably 20-30 degrees C. The preparation method of (VI) comprises reacting (V) with ammonia in presence of alkali in a closed system to obtain (VI).R = H, halo (preferably fluoro, chloro, bromo or iodo) and/or 1-3C alkyl (preferably methyl, ethyl, propyl or isopropyl); andsubstituent in N,N-disubstituted formamide = 1-4C alkyl (preferably methyl, ethyl, propyl or isopropyl).Preferred Components: The preparation method of (II) in which: the initiator is azobisisobutyronitrile, phosphorus trichloride, ammonium persulfate and/or benzoyl peroxide; the wavelength of light is 300-500nm; the mass ratio of initiator to (III) is 0.01-0.8, preferably 0.02-0.07; the molar ratio of chlorine gas to (III) is 3:1-10:1, preferably 3:1-5:1; reaction temperature is 30-180 degrees C, preferably 80-150 degrees C; and the reaction is performed in a solvent including halogenated hydrocarbon solvent and/or halogenated aromatic hydrocarbon solvent, where the halogenated hydrocarbon solvent is chlorinated hydrocarbon solvent including dichloromethane, chloroform, carbon tetrachloride and/or dichloroethane, and the halogenated aromatic hydrocarbon solvent is chlorobenzene o-dichlorobenzene, m-dichlorobenzene and/or p-dichlorobenzene. The preparation of (III) in which: the solvent is halogenated hydrocarbon solvent, halogenated aromatic hydrocarbon solvent and/or aromatic hydrocarbon solvent, where the halogenated hydrocarbon solvent is chlorinated hydrocarbon solvent including dichloromethane, chloroform, carbon tetrachloride and/or dichloroethane, and the halogenated aromatic hydrocarbon solvent is chlorobenzene o-dichlorobenzene, m-dichlorobenzene and/or p-dichlorobenzene, and the aromatic hydrocarbon solvent is toluene, o-xylene, p-xylene and/or m-xylene; the chlorinating agent is phosphorus oxychloride, phosphorus pentachloride, triphosgene, diphosgene, phosgene, thionyl chloride and/or oxalyl chloride; the molar ratio of chlorinating agent (when chlorinating agent is triphosgene) to (IV) is 0.6:1-2:1, preferably 0.6:1-1:1; the molar ratio of chlorinating agent (when chlorinating agent is diphosgene) to (IV) is 1:1-2.5:1, preferably 1:1-1.5:1; the molar ratio of chlorinating agent (when chlorinating agent is other than diphosgene and triphosgene) to (IV) is 2:1-5:1, preferably 2:1-3:1; the N,N-disubstituted formamide is N,N-dimethylformamide, N,N-diethylformamide, N,N-dipropylformamide, N,N-diisopropylformamide and/or N,N-dibutylformamide; the molar ratio of N,N-disubstituted formamide to (IV) is 1:1-5:1, preferably 1:1-2:1; and the reaction temperature is 70-120 degrees C, preferably 90-110 degrees C. The preparation method of (IV) in which the organic amine is triethylamine, tri-n-propylamine, tri-n-butylamine, diisopropyl ethyl amine, N,N-dimethylaniline and/or N,N-diethylaniline. The preparation method of (VI) in which: the reaction is performed with or without solvent; the alkali is inorganic alkali (solid or aqueous solution form) including is sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate and/or potassium bicarbonate,; the molar ratio of alkali to (V) is 1:1-5:1, preferably 1:1-2.5:1; the ammonia is ammonia gas, ammonia aqueous solution or ammonia and other organic solvent; the molar ratio of ammonia to (V) is 1:1-5:1, preferably 1:1-3:1; reaction temperature is 30-90 degrees C, reaction pressure is 0.01-1.5 MPa, preferably 0.01-0.6 MPa; and when reaction is carried out in a solvent including water, aromatic hydrocarbon solvent and/or chlorinated hydrocarbon solvent, where the aromatic hydrocarbon solvent is benzene and/or toluene, the chlorinated hydrocarbon solvent is dichloromethane; when the inorganic alkali to take part in the reaction in the form of an aqueous solution, the concentration of aqueous solution of inorganic alkali is 10-60 wt.%, preferably 20-50%; and the concentration of aqueous ammonia solution is 15-40 wt.%.