Abstract: The effect of single and combinational exposure of heavy metals, including cadmium (Cd ) and mercury (Hg), on catalase（CAT） activity in Mudsnail（Cipangopaludina cathayensis） was studied by the acute exposure experiments. The results showed that, in the experimental dose range (the concentration of Cd2+ ranging from 0.5 to 8.0 mg/L and Hg2+ ranging from 0.05 to 0.8 mg/L), when Cd2+ or Hg2+was introduced into the soil alone, low concentration of Cd2+, Hg2+ solution were found to have inductive effect over the CAT activity; while high concentration Cd2+, Hg2+ solution has, on the contrary, inhibitive effects. When exposed under Cd2+ and Hg2+ together for a certain period of time, CAT activity undergoes a significant change, which serves to explore the noxious effect of heavy metals combination of Cd2+ and Hg2+ and the CAT activity of the Mudsnail liver and pancreas and thus adopt them as the indices for indirectly testing environmental pollution.