In this paper, extraction of protease from squid viscera was studied. Factors such as the concentration of NaCl solution used in protease extraction, the ratio of squid viscera solid to NaCl solution, extracting temperature, extracting time and so on, which influenced the extraction effect, were investigated. The pH of the crude protease extraction solution was adjusted to remove impurity based upon the isoelectric precipitation principle. Various flocculants were compared in terms of their removing effect of impurity from crude protease extraction solution. Results showed that the optimal extracting conditions were as follows: the concentration of NaCl solution 0.5%, the ratio of solid to solution 1.0:1.5, ambient temperature and extraction time 60 min. Under the above-mentioned conditions, 96.06 % of total protease activity was recovered; the specific protease activity reached 1.33 U/mg. by Adjusting the pH of crude protease extraction solution to 4.5, the impurities was removed. Among various flocculants, Fe2(SO4)3 was found to be the best. By adding 1% Fe2(SO4)3 solution to crude protease extraction solution, the impurities can be removed when the ratio of crude protease extraction solution to Fe2(SO4)3 solution reaching 4:1 (V/V). Under such conditions, 80.33 % of total protease activity was recovered; the specific protease activity reached 9.37 U/mg.