Abstract: The improvement of inverse Wentzel-Kramer-Brillouin(WKB) method for refractive-index profile of a graded-index planar waveguide calculated numerically from the eigenvalue equation under the WKB approximation is extended.The Practicality of this method is demonstrated by application to three types of refractive index distribution(exponetial,Gaussian and step refractive index distribution).The refractive-index profiles caculated from the corresponding effective-index function,which can be found approximately by least-square fitting of a set of measured effective indexes,agree well with the exact profile,The absolute errors of the waveguide surface indexes calculated,with respect to the exact values,are about 0.1%.