Amid the rapid advancements in unmanned system technologies, cooperative formation control has become a key area of research in control theory. This study introduces a bearing-based formation control strategy for nonlinear multi-UAV systems, triggered by events. The strategy primarily utilizes relative bearing information between UAVs and the speed information of the lead agent, significantly reducing dependence on external hardware and the frequency of information exchange. To further optimize system performance, a distributed velocity observer was designed and integrated through an event-triggering mechanism, thereby decreasing the need for global speed information, reducing communication loads, lowering system energy consumption, and effectively saving communication bandwidth. The stability of the proposed control strategy was verified using Lyapunov stability theory. Finally, simulations in Simulink and Software in the Loop (SITL) environments further confirmed the effectiveness and practical potential of this strategy.