For improving the accuracy and robustness of the impact-angle-control guidance of air-to-surface missiles to enlarge the penetration ability against the air-defense system and the impact effect, based on the analytical solution of pure proportional navigation (PPN) guidance law against stationary targets, a three-dimensional PPN-based impact-angle-control guidance law (3D-PPNIACG) was proposed. First, based on the analytical solution of PPN against stationary targets, the guidance performance of two-dimensional PPN-based impact angle constraint guidance law (2D-PPNIACG) was analyzed, including maximum commanded acceleration, velocity increment, and capture region. Then, based on the 2D-PPNIACG and the orthogonal decomposition method of three-dimensional guidance, and with the help of the spatial geometric relationship between missile and target, 3D-PPNIACG was put forward, which can guarantee the impact-angle-control in vertical plane as well as horizontal plane. Finally, the guidance performance of 3D-PPNIACG was analyzed through numerical simulation cases, and the effectiveness and robustness of this guidance law were verified. The study and simulation results show that the proposed 3D-PPNIACG has the advantages of simple structure, ease of implementation, and good robustness, which can realize the impact-angle-control in both vertical and horizontal planes and hence has good application prospect.