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 airborne PAT system is 10μrad (1σ), and the fine tracking precision is 8μrad (1σ) 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.