Residual thermal stress of functionally graded polycrystalline diamond compact was analyzed by the finite element method with ANSYS software. It was showed that the axial tensile stress in functionally graded polycrystalline diamond compact was reduced from 698MPa to 283 MPa compared with two layer polycrystalline diamond compact, radial tensile stress was reduced from 1770 MPa to 880 MPa, and shear stress was reduced from 653 MPa reduced down to 368 MPa．In addition, the stress distribution is improved in the interface of functionally graded polycrystalline diamond compact, and bond strength are greatly increased.