  We use WKB Approximation in the calculation of slope and curvature of
Isgur-Wise function in a QCD inspired potential model.This work is an extension
of the approximation methods to the QCD inspired potential model.The approach
hints at an effective range of distance for the calculation of slope and
curvature of Isgur-Wise function.Comparision is also made with those of
Dalgarno and VIPT to see the advantages of using WKB Approximation.
