Abstract: The basic principle of a high sensitivity technique for shape measurement hasbeen described according to the theory of optical interferometry and diffraction. A newmethod is presented to eliminate the item containing coordinate variables in the formula,so that the pure contour fringe pattern can be obtained.The technique has been appliedto measure the depth distribution of a plate surface with extruded marks.Finally,thesensitivity and accuracy have been discussed,and some experimental results are provided.