Abstract: Based on optimal control theory and singularly perturbed theory,a singularly perturbed midcourse guidance law that guarantees air-to-ground missiles to ascent quickly is proposed.This new guidance law is a composite control law consisting of three parts:optimal climbing control using variable weighting factor method,minimum energy cruising phase control and minimum energy switching phase control.Moreover,a new control logic is designed in order to remove influence of climbing control on switching phase.Simulation results of a certain type of air-to-ground missile are presents.It is shown that,with simple control algorithm and feasible onboard implementation,this law not only guarantees air-to-ground missiles to ascent quickly,but also satisfies the requirements of midcourse phases.The studies have important theoretical meaning and great value of engineering application.