For the problem of trajectory planning for multi-vehicle collaborative formation in the gliding mid-flight phase, a two-phase cooperative formation trajectory planning method based on the "Coordinated Assembly and Formation Maintenance" strategy is proposed. In the coordinated assembly segment, a trajectory planning method based on a coordination-execution dual-layer framework was designed. The coordination layer included three modules: spatiotemporal capability boundary forecasting, rendezvous point information calculation and distribution, and adaptive correction of rendezvous point information, to quickly determine the rendezvous point information while considering the vehicles' control capabilities. The execution layer then designed a trajectory planning method considering spatiotemporal full-state constraints to achieve high-precision assembly of multiple vehicles, providing a favorable initial situation for formation maintaining. In the formation maintenance segment, using virtual altitude and heading angle as coordination information, a trajectory planning method based on fixed-time consistency was designed to realize long-range formation maintenance. Simulation results show that the proposed trajectory planning method demonstrates excellent high-precision assembly capability, long-range formation maintaining ability, and adaptability to multiple tasks.