The mapping satellite is use of the multichip CCD assemble technology to meet the precision landscape positioning requirements. The size of a single CCD cannot meet the requirements of modern optical system. High cost and special technology are required for the resolution. In order to apply space camera to the measurement in large field of view and high resolution, the technology of optical assembly with several CCD is discussed. And a reflector based butting system was adopted. To extend the field of view, an optical butting system is proposed. Aiming at the problems of vignette and decline of modulation transfer function caused by butting, a reflector based butting system which has nine mirrors was investigated. This paper introduced the structure design of a long array and the principle of optical butting. The basic idea of this system is to split the optical image into several parts, so that they can be detected by different sensors. The mirror is used in conventional imaging system; divide the optical image into two parts. To eliminate the vignette distortion caused by the optical system and keep high signal to noise ratio, the sensors receiving the two focal image parts are placed with a little overlapping so that they can compensate each other. In order to ensure the key techniques of mirror location accuracy, a new alignment method was proposed about locating conversation components, mainly aimed at enhancing assembly accuracy of linear array CCD.A high quality image can be obtained by butting the two image parts. Its principle, methods of adjusting and testing as well as the structure of focal plane are described. The assembly with nine TDICCDs is finished on the facility which is composed of a long work-distance microscope and a precise X-Y rail, using the method in which the mechanical adjusting is applied. Compared with convention system, this method can satisfy the linearity accuracy and overlapping pixels tolerance of 0.2 detector pixel sizes. And can meet 5um co focal accuracy; the optical assembly has the advantages of simple constitution, low cost and good adaptability, it has practical value.