A new method is used to measure the change characteristics of the lift of micro flapping wing MAV. A rectangular polyvinylidene fluoride (PVDF) film has been layout on the wing surface of miniature ornithopter as a sensor. According to the output signal of the PVDF, the lift changes of the wings of MAV are figured out. Compared PVDF data with the data of force balance; it has many obvious advantages (simple structure, fast and accurate) than the traditional ways to research the lift changes of the flapping wing MAV. Meanwhile, the lift curve of the flapping wing MAV in horizontal state and wind facing state has been studied, and the factors effecting lift of the wings by changing frequency of the flapping wing, flight speed and angle of attack of the flapping wing have also been studied.