Lift makes a vehicle in air and thrust makes advancing. The lift of flapping wing air vehicle is composed of two main parts, flapping lift and advancing lift. The advancing lift of flapping-wing is similar as of fixed-wing, generated mainly by relative velocity and angle of attack. The flapping lift is owned only by flapping wing. The flapping lift is generated by asymmetry flapping motion manner of wings, asymmetry airfoil, and asymmetry folding in flapping cycle, accordingly leading-edge vortex and wake capture effect. The thrust is completely generated by flapping wing and the magnitude of thrust is mainly controlled by flapping frequency and flapping manner. The flapping motion is a thrust generator and lift enhancing manner. Flapping wing air vehicle will be one of the star members of man-made air vehicles.