40 adult male SD rats are randomly divided into sedentary control group, low intensity group, moderate-intensity group and the high intensity group. Their SOD activity and MDA contents in skeletal muscle are measured. The results show that: soleus muscle's SOD activity and MDA content in the low intensity group are lower than those in the quiet small group, biceps SOD activity in the moderate-intensity group are more than that in the quiet small group, but MDA content has decreased. By comparing the effects of different continuous exercises on different skeletal muscle free radicals metabolism, explores reasonable exercise intensity and provides scientific methods and theoretical basis for healthy exercise.