Aiming at the problem that air-based aircraft attack the ground target with specific angles, a sliding mode guidance law is proposed to realize the angle constraint. Firstly, based on the 2D aircraft-target relative motion model, a guidance law considering impact angle constraint is designed, and based on the Lyapunov stability theory, a parameter normalized power reaching law is designed. Considering the problem of input saturation, design the adaptive reaching law parameter and introduce the limiting function to restrict the input signal to avoid the adverse effect of excessive acceleration instruction on the actuator. Considering that in the actual attack, target velocity information cannot be obtained directly by the guidance system, regard the unknown velocity information as a system disturbance and introduce the super-twisting observer to estimate it. In simulations, the designed guidance law can achieve accurate impact angle constraint when attacking stationary and moving targets and has strong practical engineering applications.