In order to analyze the variation rule and influence of the modulation in the one-dimensional phase shifting lateral shearing interferometer (PS LSI). The principle of the PS LSI based on one-dimensional Ronchi grating is researched. The inference intensity formula and intensity modulation function are reduced. By substituting the each Zernike aberration into the modulation function factor, the influence due to Zernike aberration and shear ratio are analyzed. The measurement range is mainly limited by the high order spherical aberration and large shear ratio. Finally, an experimental setup is designed to measure the wavefront aberration of a NA=0.25 microscope objective at 632.8 nm wavelength, in which using two one-dimensional gratings with 9 μm and 18 μm period respectively. The results show that when grating period is 18 μm, the measurement result is correct; when grating period is 9 μm, the reversed points exist in the modulation, the aberration is beyond the measurement range, and the correctness of the modulation function analysis result is validated.