Abstract: Aiming at the problem of the missile attacking the stationary and moving targets in the terminal guidance segment in air to ground combat, and the better constraints of the attack angle, using the traditional proportional guidance law with offsets, then doing integral calculation in the offsets, combining sliding mode variable structure theory, with product differentiation items as a dynamic sliding mode surface, a new biased proportional guidance law is designed. This guidance law has higher guidance precision and better performance when attacking ground targets. By means of Lyapunov theory, it is proved that the process of the system state trajectory reaching the sliding mode surface is finite-time convergent and stable, and its reachable condition is satisfied. Simulation results show that the new biasd proportional guidance law has better attack performance and better constraints of the attack angle.