Aiming at the problems of time-varying path constraints and unknown external interferences in unmanned helicopter formation system，this paper proposes a cooperative safety tracking control method for unmanned helicopters based on boundary protection algorithm.Firstly，for time-varying path constraints caused by external geographical environment，a new safety expectation path is designed based on a class of boundary protection algorithm.In order to counteract the impact of unknown external interferences，a disturbance observer is adopted for estimation.Then，a safety tracking controller is designed by combining backstepping control method，and the convergence of all signals in closed-loop system is proved by Lyapunov stability theory，which ensures the safety tracking performance of the unmanned helicopter formation system.Finally，the effectiveness of the proposed control method is verified by numerical simulation.