The invention relates to preparation of a compound 3,4,5,6-tetrachloro-2-cyanopyridine, in particular to a method for catching and purifying 3,4,5,6-tetrachloro-2-cyanopyridine in a gas reaction product in a gas phase chlorination process for producing 3,4,5,6-tetrachloro-2-cyanopyridine. The method comprises the following steps: (1) primary sublimation catching: a reaction gas mixture containing3,4,5,6-tetrachloro-2-cyanopyridine from a reaction bed enters a first catcher, an inert gas is introduced, the gases are thoroughly mixed and quenched to 135-165 DEG C, and sublimated flocculent crystals fall to a material outlet at the bottom of the first catcher by gravity and are discharged; and (2) secondary sublimation catching: the gas which is not sublimated in the primary sublimation catching enters a second catcher, an inert gas is introduced, gases are thoroughly mixed and quenched to 55-110 DEG C, sublimated flocculent crystals fall to a material outlet at the bottom of the secondcatcher by gravity and are discharged, and the gas which is not sublimated enters a bubbling absorber. In the invention, the solid product can be further hydrolyzed to obtain high-purity 3,4,5,6-tetrachloropyridine-2-carboxylic acid; and the invention has the characteristic of simple technique, and is easy to operate and control.