The challenge of achieving precise target impact with specific impact angle constraints in three-dimensional space for missiles was addressed. Performance limitations of traditional guidance laws under strong nonlinearity, strong coupling, and complex constraints were overcome. An impact angle constrained guidance law based on auto-coupling PD control theory was proposed. The proportional and derivative actions were coupled using a speed factor to overcome limitations of traditional PID in three-dimensional guidance. An adaptive speed factor strategy was designed to balance dynamic response and steady-state accuracy. Acceleration command saturation was introduced to handle actuator constraints. Simulation results demonstrate that the proposed auto-coupling PD impact angle constrained guidance law ensures precise target impact. Compared with an existing optimal guidance law, the proposed law enabled line-of-sight angles to converge rapidly and without overshoot to desired values. Acceleration commands remained smooth and stable during the terminal guidance phase, avoiding end-stage command abrupt changes. Good robustness and steady-state accuracy are demonstrated for different desired impact angles. The auto-coupling PD control offers an effective solution for three-dimensional impact angle constrained guidance. Advantages include relatively simple structure, fast response, high accuracy, smooth commands, and strong robustness.