Large-aperture optical telescope of next generation has two features. One is that the primary telescope is segmented, and the piston and tilt/tip errors of sub-mirrors are controlled by active optics. Another is that the adaptive optics is used to eliminate the influence of atmospheric turbulence. So it is very important to analyze the effect of segmented errors on image quality of segmented telescope for the development of next generation telescope. The effects of piston, tilt/tip and edge errors of segmented primary telescope on image quality of segmented telescope are analyzed by using the theory and numerical simulation. The results of theory and simulation indicate that the effects of piston error and tilt/tip error on image quality of segmented telescope are mutual independent, and the effect of edge error on image quality of segmented telescope is little.