Aiming at the defocusing problem of aerial photoelectric remote sensors in different working environments, a moving lens group is used to adjust the focus to ensure its imaging quality. The focusing mechanism adopts the anti-backlash screw nut pair as the transmission mechanism, adopts 6 precision bearings and elastic preload components as guide mechanism and adopts a pair of eddy current sensors and a diamond-shaped detected part as the displacement sensor to ensure the focusing accuracy to the greatest extent under the limited envelope size. The precision analysis of the focusing mechanism was carried out. And a test platform was built to carry out the transmission positioning accuracy experiment and the shaking accuracy experiment. The experimental results show that the transmission positioning accuracy of the focusing mechanism is within ±6 μm, and the shaking accuracy is within ±4″, which meets the design requirements of focusing accuracy proposed by the optical system.