Based on the traditional dynamic differential equation, an extended proportional guidance law is presented. For the sinusoidal orbital transfer motion of target after perception of danger distance, the effect of normal overload and trajectory curvature is analyzed using the extended proportional guidance law by simulation. Compared with traditional PNG laws, simulation results show that the intercept of the target based on extended proportional guidance law under the proper random quantity, when the missile is in close proximity to the target the normal overload fluctuation is improved somewhat. And interception time and normal overload have good performance. Tracking performance for high maneuverability target is better than the classical proportional guidance law.