To compensate the offset from optimal focal plane position of a space camera due to its complicated launch environment and space operating environment, a new high-precision focusing mechanism was proposed. The mechanism is driven by equal output components, transmitted by a positive and negative slider-crank mechanisms and its guiding is completed by a direct-acting component. The structural composition and motion mechanism were introduced and its error sources and influence factors were analyzed. The focusing mechanism was supported by the direct-acting component with two points and the output force of each point was equivalence, so that it has no synchronization motion error, and characterized by low internal stress in the organization and high swing angle precision. Furthermore, the gap relieving by preload was used in all kinematics pairs to eliminate the error of back lash in the focusing mechanism to improve focusing accuracy. The test parameter was tested in a simulated space environment, and the analysis and experiment results show that the focusing range of the focusing mechanism is ± 1.7 7 mm, the linear position precision and repeatability are better than ±8 μm and ±2 μm respectively, the synchronization motion error is less than ±4 μm, and the repeatability better than ±1″. In focusing travel ranges, the tilt angle accuracy of the focusing mirror and its repeatability are better than ± 5 ″ and ±1.5″, respectively. These results meet the needs of complex spatial imaging environments.