The new generation of helicopter borne air to air missile would adopt the composite guidance system, in order to improve the intercept probability at terminal guidance handover time. The main error sources of intercept probability befor the final handover time, which influenced infrared helicopter air to air missile were analyzed in detail. Based on determining the scope of the each error source, the intercept probability was analyzed through the mathematical model of practical engineering application, and the effect of error sources on intercept probability was further analyzed. It provided an important theoretical basis for the error distribution of helicopter borne air to air missile weapon system.