Abstract: longitudinal cracking is one of the most prevalent pavement distresses in the cold region of North China, which seriously damaged the durability and function of pavement. Based on the extended finite element method (Xfem), the occurrence and evolution of the longitudinal cracking in pavement induced by the settlement of sub-grade have been studied, The comparison of numerical results shows that the direct motivator of longitudinal cracking is not the heavy traffic loading although it is usually considered to be, but the settlement of sub-grade and the lateral constrains of pavement. Meanwhile, a method to simulate the settlement of sub-grade using the deducted elastic modulus of soil has been proposed. Using this method, the settlement of sub-grade could be imported to numerical mechanics tests. This study is expected to supply a new reference to predict the evolution of longitudinal cracking in pavement.