Abstract: The space camera defocus caused by temperature makes the focal plane outside the correct position range. In order to auto control the focal plane and guarantee the imaging quality, the auto- focusing system based on temperature was proposed. Firstly, the current compensation strategies of focal plane were analyzed in detail and an improvement method was presented to resolve their shortcomings and inadequacies. Secondly, the system structure and design and operating principle were introduced. Finally, the system was experimented. Experimental results indicate that the defocusing amount of camera can be controlled less than 10 um, the adjusting error of focal plane is no more than 1.3 um, and the controlling result of temperature level satisfies the requirement of system design. The auto-focusing system based on temperature can auto control temperature level, auto calculate defocusing amount, auto control focal plane and satisfiy the requirement that the focal plane of camera is inside the correct position range when camera working.