A coaxial three-mirror anastigmat system with a segmented primary mirror is modeled in Zemax. A position error correction method for segmented mirror based on sensitivity matrix retrieval is proposed. For the annular-sector segmented primary mirror, the exit-pupil aberration is fitted with annular-sector Zernike orthogonal polynomials. The sensitivity matrix of segmented mirror is calculated and the linear relationship between segment position error and exit-pupil aberration variation is verified. Simulation results show that the optical system can be recovered to the design state on condition that the segment has five corrective degrees of freedom, but small residual errors will remain in three degrees of freedom correction.