To advance the development of cooperative formation control technologies for unmanned systems, this study proposes an event-triggered direction-based formation control strategy for nonlinear multi-UAV systems. By utilizing relative directional information between UAVs and velocity information from the leader UAV, this approach reduces reliance on external hardware and decreases information exchange frequency. To further optimize system performance, a distributed velocity observer is designed and integrated with an event-triggered mechanism, thereby minimizing the requirement for global velocity information while reducing communication load, lowering energy consumption, and effectively conserving communication bandwidth. The stability of the proposed control strategy is rigorously validated through Lyapunov stability theory. Simulation results confirm the effectiveness of this strategy and demonstrate its potential for practical applications.