Abstract: Unmanned aerial vehicles (UAVs) have been widely used in the wireless communications, and are expected to play an important role in the sixth-generation (6G) wireless networks. However, due to the size and weight limitation of UAV, the system safety information capacity is limited. In addition, the broadcast and line-of-sight transmission characteristics of the wireless channel between UAVs and ground users make the air-ground communication easy to be eavesdropped by illegal ground users. To address these challenges, we adopt the wireless power transfer and physical layer security technique in this paper. We maximize the total secrecy rate over a finite time horizon by jointly optimizing the wireless charging duration, the trajectory and transmit power of the UAV subject to the energy-harvesting causal, maximuming flying speed, and limiting battery size constraints. To deal with this non-convex problem, we first transform this problem into an equivalent problem with smooth objective function, and then propose an efficient trajectory design and communications resource allocation algorithm to solve this reformulated problem by leveraging the alternating optimization and successive convex programming (SCP). Extensive simulations are carried out to demonstrate the idea and the results show that proposed algorithm outperforms the benchmark strategies without the trajectory optimization and/or power control and/or battery.