To realize the widely use of phase shift type lateralshearing interferometer in large-diameter aspherical online detection, the measuring for aspherical surface by lateral shearing interferometer was simulated to reconstruct the two dimensional surface. Shearing displacement size and sampling points numbers in the x and y direction of simulated aspheric surfaces were analysed, respectively. By using least squares method to strike waves difference and Zernike polynomial quasi to reconstruct wave-front, a non-spherical surface was simulated. The results indicate that, it′s suitable to set the shearing amount of one-tenth about the size of the aperture to guarantee high precision, and only 49 discrete sampling points are needed to display the two dimensional surface topography by using Zernike polynomial fitting.The conclusion provides a theoretical guidance for the phase shift type two-dimensional wavefront reconstruction of lateral shearing interferometry and technical support for the online practical application of large-diameter aspherical surface measurement.