An adaptive proportional guidance law with angular constraint is developed for guided bomb, which meets the requirements of strap-down seeker and penetrating attack. Firstly, a gain variable proportional navigation guidance law was derived by classical proportional navigation and desired impact angle. Then, a closed-loop correction of guided coefficients was proposed for the sake of robustness enhance-ment of the guidance law. Simulation studies show that the presented guidance law can implement efficiently the angular constraint mission as well as preferable guidance precision.