TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The catalyst comprises palladium carbon, palladium hydroxide, palladium black, platinum oxide, Raney-nickel, or nickel base composite catalyst Urushibara nickel, preferably palladium carbon and Raney-nickel. The dewatering agent comprises phosphorus oxychloride, thionyl chloride, phosphorus pentoxide, or polyphosphoric acid. The amount of dewatering agent is 1-7 times preferably 2-5 (v/w) of feeding quantity of 4-chloro-2-amino-1,2-phenyldiazosulfide.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method also comprises adding heterogeneous catalyst into solvent; filling hydrogen until certain pressure is reached via 4-chloro-2-nitro-aniline as raw material; and reacting at certain temperature to obtain 4-chloro-1,2-phenylenediamine. The hydrogen pressure is 0.2-5 MPa. The reaction is carried out at 25-120 preferably 40-80 degrees C. The method also comprises adding heterogeneous catalyst into solvent; filling hydrogen until certain pressure is reach; and reacting with 4-chloro-3-nitro-1,2-phenyldiazosulfide at certain temperature to obtain 4-chloro-2-amino-1,2-phenyldiazosulfide. The method also comprises adding dewatering agent to solvent after heating and reacting 4-chloro-2-amino-1,2-phenyldiazosulfide and 1-benzoylimidazoline; adding water containing soda; and hydrolyzing to obtain tizanidine hydrochloride. Preferred Component: The solvent comprises water, methanol, ethanol, ethyl acetate, isopropanol, ethylic acid, and/or tetrahydrofuran, preferably methanol or ethanol. The solvent which is added with dewatering agent comprises N,N-dimethylacetylamide, acetonitrile, dichloromethane, dichloroethane, and/or trichloroethane, preferably methylbenzene, dimethylbenzene and N,N-dimethylformamide. The amount of solvent is 2-10 times preferably 3-6 times (v/w) of feeding quantity of 4-chloro-2-amino-1,2-phenyldiazosulfide. The dewatering agent can be oxalyl chloride, trifluoromethane sulfonic anhydride, or tripolycyanacyl chloride.