A wireless sensor network's (WSN's) uptime is highly depended on the lifespans of its wireless sensor nodes (SNs). However, the battery of an SN sometimes may not be easy to be replaced owing to circumstantial constraints. Nowadays, the far-field wireless power transmission (WPT) has attracted more attention from industry and academy. Many researchers have proposed to utilize the WPT technology to remotely charge the SNs. As unmanned aerial vehicle (UAV) can fly close to the SNs located in some hard-to-reach areas, in this work, a UAV is adopted to assist the green base station (GBS) to efficiently power the SNs which are far away from the GBS. Considering the limited energy carried by the UAV and the UAV's energy consumption, we propose a novel UAV comprehensive charging strategy to efficiently power the WSN and to enable all the SNs to be charged with considerable energy replenishment. The simulation results validate our proposed strategy can effectively extend the WSN's uptime.