Abstract: This paper presented a Williams element with generalized degrees of freedom (GDOFs) for stress intensity factor (SIF) analysis of reflective crack in asphalt pavement on semi-rigid base course by means of the layered linear elastic plane strain model and isoparametric element.The stiffness equation was developed for Williams element with GDOFs to yield directly the SIF at the reflective crack tip in the asphalt pavement,as the Williams element contains parameters related to the SIF.The SIF variation is investigated during the propagation of reflective cracking under symmetrical and partial load respectively.The influence of the material and geometrical parameters on the SIF was discussed in details.Numerical example shows that the Williams element has the advantage of simplicity as well as high accuracy.Results from the Williams element agree well with those by the traditional quarter-point element,therefore Williams element can be used for SIF evaluation at the reflective crack tip in the asphalt pavement on the semi-rigid base course.