Fixed-wing drones have strategic advantages in military missions for gathering intelligence and monitoring enemy activities. This paper investigates a trajectory planning method of fixed-wing drones suitable for performing multi-phase cruise missions. Firstly, the fixed-wing drone system dynamics are modeled. Secondly, the fixed-wing drone multi-phase cruise mission trajectory planning problem is established by combining path constraints, inter-segment connection constraints, and endpoint constraints. Finally, the trajectory planning problem is solved by Matlab GPOPS general-purpose software, and the simulation shows the effectiveness of the trajectory planning method.