we have modeled a segmented mirror optical system by software zemax, and analyzed influence of segmented mirror's position error to the optical system imaging for the first time to author's best knowledge. the primary mirror is composed of 18 segmented mirrors. by adjusting each one's position error of six freedoms, we get six relationship curves between position error and the optical system's image quality. the relationship curves show that some have different wave-front error rms values when segmented mirrors have same position errors. the middle mirrors are sensitive to the movement along x axis direction, and the outer ones are sensitive to the movement along y axis direction. the middle ones and outer ones are all sensitive to the tilt error, especially tilt along x, y axis. (c) 2017 elsevier gmbh. all rights reserved.