To meet the requirements of missile with terminal-attack-angle constraint in modem battlefield, an adaptive guidance law with terminal attack angle constraint was derived. A guidance model was deduced in the two-dimensional coordinate system by considering the LOS angles and its change rate as state variables. A guidance law with terminal-attack-angle constraint was designed by adopting an adaptive reaching law. An extended state observer was adopted to compensate the target maneuvering. The simulation results show that the guidance law can be used to hit the target with expected terminal-attack-angle. The guidance law has robustness for target maneuvering, and it meets the requirement of zero miss amount.