Abstract: AIM:To offer the method of calculating infection rate and number of infected persons in nation wide sampling investigations on schistosomiasis japonica. METHOD: Calculation formulae were established on the basis of schistosomiasis epidemiology and biomedical statistics, adopting multiple stratified cluster sampling. RESULTS: Thirteen formulae were derived for calculation of infection rate and number of infected persons in different endemic provinces with different types of endemic areas. CONCLUSION: The presented method is simple, rational and available.