Abstract: To improve guidance precision and to ensure the ideal damage effect, an approximate vertical diving attacking guidance law of air-to-ground weapons is proposed. Based on the relative motion model for a missile and target in a two-dimensional plane, the impact angle constraints are transformed to control the terminal line of sight. According to final the position and the impact angle constraints, a sliding model variable structure guidance law that includes four guidance parameters is designed： the angle error parameter, the switching parameter, the reaching law parameter, and the constant parameter. The basis for the parameters selection is obtained by analyzing the influence of four guidance law parameters on guidance performance. The simulation is demonstrated for the designed guidance law to obtain a near zero miss distance and a 90° impact angle. The miss distance is decreased by 87.43% and the impact angle is increased by 47.01% in comparison with the proportional guidance law.