To improve the bearing capacity of existing cement concrete pavement and prevent reflective cracking, HMA overlay with SAMI has been used in some airport. The aim of this paper is to evaluate the performance of such structure with 3D FEM quantitatively. Through dynamic and static analysis with 3D FEM, the finds are obtained: (1) the detrimental load position is the edge of joint, but the effect of joint on the structure is smaller and smaller with the increase of overlay's thickness; (2) split strength is an effective criterion to evaluate the overlay's thickness, but also it can interpret the reason that it can prevent the reflective cracking.