An atomistic model for annealing simulation is presented. To well simulate both BED (Boron Enhanced Diffusion) and TED (Transient Enhanced Diffusion), the surface emission model, which describes the emission of point defects from surface during annealing, is implemented. The simulation is carried out for RTA annealing (1000 or 1050) after B implantation. The implantation energy varies from 0.5 keV to 13 keV. Agreements between simulation and SIMS data are achieved. Both BED and TED phenomena are characterized. The Enhancement of diffusion is discussed. The surface emission model is studied by simulation. The results shows that the surface emission has little effect on annealing of B 10 keV implantation while obvious effect on annealing of B 0.5 keV implantation. It indicates that the surface emission is much more necessary to simulate BED than TED.