The development of large particle synthetic diamond technology makes it feasible technically and economically to manufacture surface set diamond bit. In this paper, numerical simulation study on the force, flow field and temperature field of φ75mm surface set synthetic diamond bit were made. The results indicate that diamond particles will be easily carbonized in the conditions of high bit weight and without drilling fluid circulation. With the cooling effect of drilling fluid, bit would get refrigeration in 0.006s during one round of bit rotation in 0.08s. Meanwhile, the erosion effect on bit body by hydraulic cavitation and solid particles in drilling fluid is very obvious. Duo to micro cracks in diamond particles, damage could occur in diamond particles even under the allowable stress. The comparative analysis shows that the diamonds on the outermost and the innermost nozzles of surface set diamond bit are prone to be damaged, so the design and manufacturing of surface set diamond bit should be strengthened.