Abstract: The 3D elastic mechanics and finite-element structure analysis priniple were provided. The mechanics characteristics of the three-faced aluminous rotating mirror were analyzed, and the finite-element model was established. The stress distributions of the tri-face aluminous mirror were presented under three fits of the shaft and axle hole. The simulation results indicate that the fit modes affect the mirror structual strength little, but the axle hole weakens the structual strength obviously. The improved structure which diminishes the inner stress of the rotating mirror was presented, whose structual strength is 2.9 times and the utmost linear rate is 1.7 times of the old one, so it is more propitious to the frame-camera.