Abstract: In this paper, firstly, the acute toxicity of triazopnios with different density on Charybdis japonica was determined, and we obtained that the safety concentration was 0.27 mg·L^-1. And secondly, effects of 0.27 mg·L^-1 triazopnios accumulation on protective system in 5 tissues (muscle, gill, hepatopancreas, heart and sex gland) were studied. The results showed as follows: (1)Enzymes of protective system of C.japonica included SOD and CAT, and POD was not detected and measured in those tissues.(2)SOD and CAT activities exhibited significant differences among different tissues, and the orders of SOD and CAT activity from high to low were heart > gill and muscle > sex gland and hepatopancreas, sex gland > hepatopancreas > heart > gill and muscle, respectively.(3)SOD and CAT activities in test group would change relatively when compared to the control group. Low levels of the chemicals could stimulate SOD and CAT activity, while the activity would decrease with high level. (4) The sensitivities of SOD and CAT to the poison in gill, sex gland and hepatopancreas were much more than those of heart and muscle.