The invention belongs to the technical field of organic synthesis, and provides a new synthesis method of phenylguanidine bicarbonate. The method comprises the following steps: carrying out a reaction on aniline as an original raw material and the carbon dioxide to synthesize the phenylamine bicarbonate, and then enabling the generated phenylamine bicarbonate to react with a cyanamide solution under the carbon dioxide system to synthesize the phenylguanidine bicarbonate. The carbon dioxide system is adopted for synthesis, the production cost is greatly lowered, the reaction steps are reduced, the product content and yield are improved; and meanwhile, the carbon emission is reduced, and the environment is protected.