The working environment of the lightweight dual-band aerial camera is very complicated. Due to the changes in the environment, the focal plane of the camera will produce different degrees of deviation. In order to ensure the imaging quality of the camera in the complex environment, it is necessary to correct the focal plane of the camera, so a focusing mechanism is designed. The transmission mode of the focusing mechanism is a worm-ear and a eccentric cam. The rotation of the eccentric cam drives the focusing lens moving along optical axis direction to solve the problem of aerial camera defocus. The optimized focusing mechanism has a shape size of 96 mm×65 mm×62 mm. The precision analysis of the focusing mechanism is carried out in the effective working range. The transmission precision experiment and the sway precision experiment are also carried out. The experimental results show that the transmission precision of the focusing mechanism is 3.5 μm, and the maximum sway error is below ±3″. The focusing mechanism meets the requirements of the structure space size and focusing precision.