The main method to improve the resolution of optical system is enlarging the pupil of the optical system, and segmenting sub-mirrors to get an equivalent large diameter primary mirror is a common way to enlarge clear aperture. After the deployment of sub-mirrors for segmented mirrors optical system on orbit, there is deviation between deployment position and the designed position, which is called position error. The error determines the imaging quality of the optical system. So it is necessary to analyze the precision of the position of sub-mirrors. Optical software is used to model the segmented mirror optical system, and the relationship curves between position error and the system′s imaging quality is got by adjusting position error of six degrees of freedom for sub-mirrors. The results show that root mean square (RMS) values generated by the same position error are different when sub-mirrors are at the different positions. The middle mirrors are sensitive to the movement along X axis direction, and the outer ones are sensitive to the movement along the Y axis direction. Two methods are used to distribute the errors into the sub-mirror position error. One is distributing the position error to each sub-mirror alone. Another is distributing the same position error to each sub-mirror. The results show that the former way has a more relax position error when the generated wavefront errors are the same.