TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method comprises (i) adding p-nitrotoluene into a reactor, adding natural water, stirring with a stirrer at a rotating speed of 25 revolutions/minute, performing steam heating, measuring and controlling the temperature at 70-80 degrees C under atmospheric pressure, slowly adding bromine, hydrogen peroxide and dihexyl peroxydicarbonate into the reactor and reacting for 2 hours to obtain nitrobenzyl bromide; (ii) taking the mixed solution of bromide obtained in the step (i), pumping into a second reaction kettle, raising the temperature to 90 degrees C under atmospheric pressure, stirring with a rotating speed of 35 revolutions/minute, adding aqueous sodium carbonate solution, reacting for 1 hour to obtain nitrobenzene-methanol mixed solution by organic phase (water-insoluble) and aqueous phase (water-soluble), processing liquid-liquid separation, conveying organic phase containing nitrobenzene-methanol into next step, recovering solvent by distillation, entering the aqueous phase of alkaline aqueous solution of sodium bromide and a small amount of sodium carbonate into an alkali storage tank and entering the small amount of carbon dioxide generated into alkali liquor absorption pool; (iii) pumping the organic phase containing nitrobenzene-methanol into a third reactor, stirring with the rotating speed of 30 revolutions/minute, raising the temperature to 80-90 degrees C under atmospheric pressure, adding nitric acid and solid catalyst to react for 1.5 hours to obtain a mixed solution of o-nitrobenzaldehyde, and adding the organic phase into a fourth reactor, where the aqueous phase is low-concentration waste nitric acid solution, which enters into the acid storage tank to produce small amount of nitrogen dioxide, and enters into alkali liquor absorption pool; and (iv) maintaining the fourth reactor at room temperature under atmospheric pressure, stirring at a speed of 25 revolutions/minute, adding aqueous sodium hydroxide solution, water and aqueous hydrochloric acid solution into the organic phase, reacting for 0.5 hours to obtain solid-liquid mixed solution, discharging into a solid-liquid separating device for separating the o/p-nitrobenzaldehyde phase, vacuum drying and packaging.