Aiming at the problem of guidance law design for intercepting stationary or slowly moving targets with the impact angle constraint, Based on the missile-target dynamics in the plane, a guidance law is designed considering missile’s autopilot lag using the sliding mode variable structure and nonlinear back-stepping control methods. The missile’s dynamics of autopilot can be approximately described as a first-order process, meanwhile, the chattering phenomenon of sliding mode is weaken by the integrated application of high gain saturation function and improved variable switch term. Line of sight angle rate will converge to zero ultimately and the trajectory inclination angle will ultimately converge to the desired value, respectively. Simulation results show that the guidance law can be used to hit the targets with desirable impact angle and the influence of the autopilot lag on guidance accuracy can also be compensated, which has good adaptability and robustness against the changes of the parameters and external disturbances. The research can offer some references for practical engineering application.