Segmented errors have important influence on the image quantity of segmented mirror. The complex amplitude distribution of reflected lightwave corresponding to single segment was given based on the scalar diffraction theory. The analysis model which characterized the impact of segmented errors was established by processing the segmented errors through coordinate transformation method. The Point Spread Function (PSF) and Strehl Ratio (SR) curves corresponding to various segmented errors were got by numerical simulation. The results show that SR curves corresponding to piston errors are periodic. The SR curves corresponding to tip-tilt errors and segment gaps have same structures. The conclusion provides a support for the image quantity analysis of segmented mirror.