It is very important to improve the penetration depth and fueling efficiency of supersonic molecular beam injection (SMBI) especially for the next generation fusion devices such as ITER.Two components,a fast component (FC) and a slow component (SC),have been observed in the HL-2A SMBI experiments for several years,and the FC can penetrate much more deeply than the common SMBIs which draws a great deal of attention for a better fueling method.It is the first time to the FC and SC of SMBI have been simulated and interpreted in theory and simulation in this paper with the trans-neut module of the BOUT++ code.The simulation results of the FC and SC are clear and distinguishable in the same way as the observation in experiment.For the major mechanism of the FC and SC,it is found that although the difference in the injection velocity has some effect on the penetration depth difference between the FC and SC,it is mainly caused by the self-blocking effect of the first ionized SMB.We also discuss the influence of the initial plasma density on the FC and SC,and the variation of the SC penetration depth with its injection velocity.