A computer-based method for measuring the local refractive index gradient of phase objects using the projection moire´ technique is presented. A phase object is placed in front of the projected grating pattern. The image of the projected grating pattern deforms in accordance with the variation of the refractive index of the phase object. The moire´ fringe is generated by superimposing two images of the projected gratings pattern (the original pattern and the deformed pattern). The optical transmission characteristics of projection moire´ fringe is discussed. The moire´ deflectogram is analyzed by Fourier filtering and the phasemeasuring technique.