Space remote sensing camera in the launch process and its in-orbit operation, due to environment change of atmospheric pressure, temperature, mechanics, results in focal plane defocus. In order to meet the requirements of imaging quality, the focal plane must be corrected before putting it into use. For meeting the features and imaging quality requirements of lightweight and miniaturization space camera, the focusing mechanism was designed, the motion displacement was in the range of ±3 mm, and the weight was only 3.25 kg. The self-locking property of the worm drive mechanism was used to prevent the movement of focal plane in the external forces. Micro-precision linear rolling guideway was selected to ensure the linearity accuracy of CMOS target plane. At the same time, photoelectric encoder (16 bit) was used to real-time feedback the positioning information of target plane, forming a closed-loop control to ensure its positioning accuracy. And, the theoretical calculations, dynamic analysis and experimental verification, accuracy testing and analysis, calibration test of focal plane were worked out. Experimental results indicate that the first natural frequency of focusing mechanism is 182.7 Hz, it can effectively avoid the resonance phenomenon. And the linearity accuracy of CMOS target plane is better than 20″, the positioning accuracy is better than ±4.2 μm, meeting the focusing accuracy. Simultaneously, calibration experiment of focal plane verifies the designed effectiveness of the focusing mechanism, meeting the imaging quality of space remote sensing camera.