An amide dehydration method adopted for synthesizing piperonylonitrile can generate a large quantity of waste acid, and with respect to adopting a catalytic dehydrogenation method of a copper catalyst, the reaction conditions are harsh and the reaction yield is low. Therefore, the invention provides a method for synthesizing the piperonylonitrile by using heteropolyacid as a catalyst, and the method comprises the following steps: taking phosphotungstic acid (H3PW12O40) and phosphomolybdic acid (H3PMo12O40) as main raw materials to synthesize a heteropolyacid catalyst; taking xylene and piperamide as raw materials to synthesize the piperonylonitrile under the catalysis of the heteropolyacid catalyst. The method adopted for synthesizing the piperonylonitrile has the advantages of having fewer three wastes and mild reaction conditions, being suitable for large-scale industrial production and the like.