Abstract: In this paper,the head of silver carp,the most important part of fish byproducts were taken as raw materials. The hydrolysis effects of papain,trypsin,flavourzyme,neutral protease and alkali protease were compared and selected,with the content of amino nitrogen in the hydrolysate as an index. The hydrolysis process was optimized by orthogonal tests on the basis of single factor,and the composition of free amino acid in hydrolysate was analyzed. The results showed that trypsin could be selected as the best hydrolysis enzyme,and the maximal content of amino nitrogen in hydrolysate reached 63.69 mg with the following conditions:hydrolysis temperature of 55 ℃,p H8.0,the ratio of water to materials 1∶3,enzyme concentration 80 U/g,and the content of free amino acid in hydrolysate was higher.