On the basis of chlorine disinfection,chemical agents are gradually added to form a mixed disinfectant composed of hydrogen peroxide,sodium hypochlorite and ozone.The killing effect of the mixed disinfectant on Bacillus subtilis spores was studied through experiments.The results showed that adding ozone on the basis of sodium hypochlorite increased the overall killing effect by 0.524 log,while adding hydrogen peroxide on the basis of two-component mixed disinfectant increased the overall killing effect by 0.337 log.When the added amount of hydrogen peroxide in this three-component mixed disinfectant is 0.25 mg/L,the overall killing effect is the best,which can reach 1.959 log,that is,the killing effect for Bacillus subtilis,a substitute microorganism for"two insects"(Cryptosporidium and Giardia),is close to 99%.