In this paper, we propose an event-based obstacle avoidance control method that enhances the security of unmanned aerial vehicle (UAV) time-varying formation (TVF) under Denial of Service (DoS) attacks. Network security challenges are escalating in severity. Cyber-attacks significantly impact the flight safety of UAV TVF that rely on link communications for stability. Particularly in environments with obstacles, malicious attacks that hinder UAV communication can trigger chain collisions. A novel TVF control method grounded in event-triggering and the artificial potential fields (APF) approach is introduced. Without cyber-attacks, the proposed control method ensures that UAV TVF maintain their desired configurations and remain collision-free. Furthermore, during DoS attacks, we employ a non-cooperative obstacle avoidance strategy where neighboring UAVs are treated as obstacles. This approach ensures collision-free flight, even when communications are compromised. We verified the efficacy, correctness, and superiority of our proposed method through simulation. In conclusion, our proposed method bolsters the safety, reliability, and efficiency of TVF, offering robust theoretical backing for advancing unmanned system technology.