Free-space laser communication is characterized by high communication speed,strong anti-jamming ability,high confidentiality,and flexible configuration.In this paper,a pointing,acquisition,and tracking (PAT) system based on a two-stage (i.e.,coarse and fine) composite tracking mechanism is proposed to solve the optical axis alignment problem,which is common in free-space laser communications.The acquisition probability of the PAT system is ensured by designing two tracking modules,a coarse tracking module which combines passive damping with active suppression and a fine tracking module based on an electromagnetic galvanometer.Both modules are combined by using a dynamic scanning mechanism based on the gyroscope signal.Finally,a free-space laser communication test with a long range and a high speed is conducted by two fixed-wing Y12 aircrafts equipped with the proposed PAT system.Experimental results show that the coarse tracking precision of the airboe PAT system is 10 μrad (lσ),and the fine tracking precision is 8 μrad (lσ) during flights which are much improved as compared with the indoor tests.This indicates that the system can achieve a high precision for PAT during high-speed and long-range laser communications in the free-space.This also verifies the tracking capability and the environmental adaptability of the proposed laser communication PAT system.