A technique for accurately measuring the wavefront aberration of aspherical optical surfaces with a lateral-shearing interferometer is described. A computer-controlled interference phase measuring technique is employed, which provides greater accuracy and real-time data analysis. Key elements of the present system are a lateral-shearing interferometer with a parallel plate, a piezoelectric-driven mirror, an areal image detector, and a microcomputer system with a graphic display. The shearing interferometer gives a fringe pattern corresponding to the derivative of the wavefront, which is analyzed by the fringe scanning method. By integrating the derivative of the analyzed data, we have the wavefront aberration of the test optics over an aperture containing a 32 X32 element array. A rms accuracy of measurement of 1/32 wavelength is achieved on the evaluation of an f/4 aspherical mirror.