The invention relates to a synthesis method of Beta-amidocyanogen carboxylate, and aims at providing the synthesis method for obtaining Beta-amidocyanogen carboxylate through the addition between amine compounds and Alpha, Beta-unsaturated carboxylate in pure water by taking phosphotungstic acid as catalyst. The synthesis method comprises the following steps: firstly, the amine compounds and Alpha, Beta-unsaturated carboxylate are mixed, and the pure water is added and used as solvent; phosphotungstic acid, the valent weight of which is 0.005 to 0.015, is used as the catalyst and added in the mixture, and the reaction lasts for 4 to 40 hours through stirring under the temperature ranging from 25 to 90 DEG C; the molar ratio among the amine compounds, Alpha, Beta-unsaturated carboxylate and the catalyst is 1.2:1:0.005 to 0.015; secondly, after the reaction is completed, ethyl acetate is utilized to extract reaction liquid, an organic layer is merged, and the liquid-separation is performed to remove a water layer; thirdly, the organic layer is washed by saturated sodium carbonate solution and saturated sodium chloride solution in turn, and a crude product is obtained through drying, filtering and decompression as well as exsolution by using anhydrous magnesium sulfate; finally, pure Beta-amidocyanogen carboxylate is obtained by separating the crude product through column chromatography.