Abstract: Highly concentrated stress near the interface on both sides of brazing seam tip is the main reason for fracture failure of polycrystalline diamond compact (PDC) bits. On the basis of ANSYS, numeric simulation was conducted for brazing crack of PDC bit. Aiming at different shape, thickness and position of brazing seam, stress field contours and stress intensity factors were calculated at the tip of cracks. With aide of this new method for calculation of stress intensity factor, the paper described the mechanism of PDC fracture failure to guide the welding process, stabilize and improve the quality of welding PDC bits.