Abstract: The enzymolysis of the Mactra veneriformis was studied by measuring the amino nitrogen content and the recovery of nitrogen in the hydrolyzed solution under different conditions. The protein of Mactra veneriformis was hydrolyzed by several kinds of proteinase. Contrast experiment was designed to determine the best incision enzyme and excision enzyme of in-outside two steps enzymolysis. The optimized condition of neutral protease and complex protease was chosen by single-factor and orthogonal experiment. The optimal condition was that the 1500U/g neutral protease was added first for the enzymolysis for 6h in the condition of 45℃, pH7.5 and solid-to-liquid 1∶3 (g/mL) , and then 4200U/g complex protease was added for the enzymolysis for 11h in the condition of 45℃ , pH7.0 and substrate concentration 1 ∶3 (v/w ) . Under this condition , the combination between neutral protease and complex protease had good hydrolysis effect on mactra veneriformis, the amino nitrogen content was 20.78mg/g and the recovery of nitrogen was 88.19%.