Some mathematics models are made to analyze some important errors in this paper firstly, and the result shows that the most important error is the measurement error of interferometer. Then the way in which the error of interferometer influences the accuracy of stitching is studied. The matrix singular value decomposition (SVD) is introduced in this paper to deal with the ill-conditioned equation series to reduce the effect of the most important error, while the contrast data is done with QR arithmetic. The result reveals that the SVD is useful in high accuracy sub-apertures stitching, and can decrease the requirement to high accuracy equipment.