Reinforced gabion is a man-made material commonly used in closure, blocking and revetment projects. Exploring its stability mechanism is of vital significance to guiding its application. In this research, tests on the incipient motion of reinforced gabion of different shapes and void ratios were performed. Results suggest that given the same other influential factors, larger void ratio leads to better stability. The stability of reinforced gabions varies with different shapes. A formula of the incipient velocity of reinforced gabion in consideration of void ratio, size, density, shape, relative roughness and other factors was proposed to supplement and improve the classic formula, and is verified to be of good accuracy.