In this study, byproducts of crucian were used as the raw materials to prepare angiotensin converting enzyme (ACE) inhibitory productsthrough enzyme hydrolysis. On the basis of the inhibitory rate of hydrolysate, pepsin was identified as the optimal enzyme from alkaline protease, flavor protease, neutral protease, trypsin, papain, and pepsin. On the basis of single factor experiment, the optimal hydrolysate conditions of crucian were obtained through Box-Benhnken central combination design and RSM. Simulating the prediction model of quadratic equation, the optimal enzymatic hydrolysate conditions were liquid-material ratio of 14.4(mV), hydrolysis concentration of \[E\]/\[S\]=521 U/g, hydrolysis time of 5.3 h. Under the optimal conditions, the ACE inhibitory rate of enzymatic hydrolysate reached up to 72.34%, it was in close agreement with the predicted values of 76.17%.