In order to achieve the intercept mission requirements， an improved optimal guidance law is derived considering the angle constraint of the interceptor and the premature loss of energy that cannot satisfy the subsequent interception requirements. Based on the structure of energy minimum objective function， a control weighted function is proposed to minimize the required overload in the initial phase and the terminal line of sight （LOS） angle can converge to the excepted value. An angle constraint optimal guidance law is derived in view of small angle assumption and optimal control theory. Based on the characteristics that the guidance law can make the terminal LOS angle converge， the problem of terminal LOS angle is converted into the problem of terminal encounter angle， and the optimal guidance law with terminal-intersection angle constraint is obtained. The simulation results show that the designed guidance law can not only realize terminal encounter angle control， and also ensure low energy consumption in the initial stage of guidance， as well as achieve high hit accuracy. The designed approach has certain reference and application values for the study on the optimal guidance law of interception missile.