空间相机调焦技术关系着相机的成像质量，为空间相机在轨测试中的一项关键技术。基于图像评价的调焦技术，结构简单，集成度高，在空间相机中已经得到了应用。其关键技术是要建立调焦评价函数。调焦评价函数是指导调焦过程的依据。阐述了造成相机离焦的主要因素，在调研分析国外相机调焦评价函数的基础上，对调焦评价函数的选用原则进行了归纳，并介绍了常用调焦函数的基本形式和优缺点，为相机调焦技术的研究提供借鉴和帮助。

Focusing technique of space camera has relation to camera image quality, being one of the key technologies of on- orbit test of spacecamera. Image based focusing technique with simple structure is highly intergrated, which is used in space camera. The key of Image based focusing is to estabilish focusing evaluation function. Focusing evaluation function can provide guidance for the focusing process. This paper discusses the influence caused by defocus. Based on the study on focusing evaluation function methods of foreign space camera, some instructional conclusions about choosing focusing evaluation function method and advantages and disadvantages are obtained, which provide reference and help for space camera focusing technique.