Based on the theory of aperture diffraction, a set of co-phase error optical detection system with segmented mirrors is designed, and the dual-wavelength narrow band co-phase algorithm is used to realize the co-phase detection of synthetic aperture segmented mirrors. In the scheme, circular aperture mask plate, phase difference plate and prism array have been designed for the system. By numerical simulation, a set of template pictures about the circular aperture diffraction with a series of different optical path differences have been obtained. Then, the correlation of the test image and template pictures will be figured out to calculate the optical path difference of the two adjacent sub-mirrors. Before applying the scheme to the segmented mirror detection, a known amount of phase difference in the optical path is introduced by phase plates to carry out the simulation, so that the diffraction patterns are sampled and matched. Results of the experiment verify the feasibility of the scheme, and high accuracy co-phase detection of the synthetic aperture segmented surface can be realized.