In order to solve the problem of the precision guidance of the air defense missile of the infrared imaging guidance,the sub-optimal variable structure guidance law,is deduced,which is based on the theory of the optimal control,sliding-mode variable structure control and parallel approach. Through the comparative test,the simulations show the excellent performance of the guidance law.During the missile guidance,we needn't know the precision the acceleration and velocity of the target,so the guidance law can be used in the infrared imaging missile.