Abstract: Due to the relative posture of each subaperture measurement is not known exactly, there is some ambiguity when the individual annular subapertures are combined into a full aperture map. To reduce this ambiguity resulted from mechanical errors, a global optimization algorithm separating mechanical errors was proposed. This algorithm established a mathematical model for separating mechanical errors based on wavefront aberration theory, and used ray tracing to eliminate the difference between ideal aspheric wavefront and reference spherical wavefront in every annular subaperture. Based on the global optimization algorithm which could abstain error transfer and accumulation， and each measured subaperture phase subtracted corresponding calculated difference firstly, and then these subaperture phases were stitched into a full aperture map by this algorithm containning mechanical error separation. A paraboloid with aperture of 75 mm and vertex radius of 100 mm was tested by annular subaperture stitching interferometry, the error of peak-valley was 0.05 , and the root-mean-square error was 0.003 . Results indicate that the global optimization algorithm can effectively separate and compensate mechanical errors.