Abstract: Objective In order to evaluate the effect of 7 times strengthened National Immunization Days Activies(NIDs) in Liaoning Province,We analyzed the data of NIDs.Methods Comparative analysis by using of epidemiological method.Results the coverage rate of 7 times NIDs Liaoning Province was above 96%.At present,the children of OPV "zero dose" have been decreasing,and theirages were under 1 year old.Based on birth-co-hort analysis,a certain proportion of children missed by each NIDs,and the proportion of children being missed decreased as the childrencs age increased.Conclusion So maintaining the NIDs activities have controled the childrencs accumulation of OPV "zero dose",most raised immunitied level of proportion,timely prevent the spreading from wild polio.