Space cameras are extremely vulnerable to the offset from its optimal position to the focal plane because of its complicated launch environments including shock, vibration and overload, and space operating environments, such as high vacuum, low temperature and micro-gravity. To improve the imaging quality, a new high-precision focusing mechanism for effectively compensating this offset was proposed to improve the adaptability of a camera by steering screw pairs, guiding parallel guide tracks and driving inclined-guides. In the design, schemes of anti-cold welding, gap relieving by preload and double anti-seize were adopted to improve the structural strength, rigidity and reliability and to guarantee the focusing precision. The structure and working principle of the mechanism were introduced and the design scheme for system reliability was described, then a synthetic test was performed. The test results show that the accuracy of linear movement and repeatability of the mechanism are less than ±2 μm and ±1 μm respectively, and the swing of the focusing mirror around X and Yaxes in the total focusing range are both less than ±3.5″, which meets the requirements of the users.