In unmanned aerial vehicle (UAV) enabled mobile edge computing (MEC) system, rotary-wing UAV can be dispatched to fly close to ground terminals (GTs) to execute their offloaded tasks. This can extend GTs’ computing capability and save their energy cost. However, to enhance the energy efficiency of UAV propulsion, ensure successful completion of each GT's mission, and maintain a stable UAV-GT uplinks, it is crucial to design a rational UAV 3D trajectory and mission offloading strategy.