Sub-aperture stitching algorithm should compensate the mechanical location errors in sub-aperture stitching interferometer because they lead to the relative location errors between sub-apertures which affect the stitching result. In order to improve the compensation ability of sub-aperture stitching algorithm, a new stitching algorithm different from the calculation compensator algorithm using original pictures is proposed. The new algorithm transforms original pictures into images beneficial to the calculation of compensator and calculates the location of each sub-aperture using pictures after transformation. It stitches original pictures using the calculated locations. Due to the high location accuracy of the sub-aperture stitching interferometer, the new algorithm transforms original pictures to gradient norm pictures and gradient direction pictures, and calculates the compensator based on direction pictures using norm pictures as weight. The simulation result shows that this algorithm compensates location errors more effectively than the calculation compensator algorithm does. In comparison with full-aperture testing, sub-aperture stitching result demonstrates the validity of this algorithm, and indicates that the method can enhance the location errors compensation ability by choosing a proper transformation.