The invention provides preparation methods of p-chlorobenzonitrile and p-chlorobenzamide, and belongs to the technical field of organic chemistry, further to the technical field of organic fine chemicals. The p-chlorobenzonitrile preparation method comprises: generating a p-chlorobenzonitrile-containing mixture by using a p-chlorobenzamide dewatering reaction, carrying out pressure reducing distillation on the p-chlorobenzonitrile-containing mixture to obtain crude nitrile, carrying out water washing on the crude nitrile, filtering, drying, and carrying out pressure reducing distillation to obtain a finished product p-chlorobenzonitrile. According to the present invention, p-chlorobenzamide is generated by carrying out a reaction on p-chlorobenzoic acid and ammonia, wherein p-chlorobenzoicacid and ammonia are used as raw materials, and are subjected to a series of reactions to generate p-chlorobenzonitrile, such that the whole reaction process is continuous and controllable, and the route is short; and the whole reaction process recovers and utilizes the unreacted raw material and the intermediate product so as to reduce the emission of three-waste, achieve the safe, clean and environmentally friendly production and significantly reduce the production cost.