Numerical simulation of the wall-impingement mixing process of a diesel fuel spray on the plane with a BUMP was carried out by using standard turbulence model and PISO algorithm. The computed results were in good agreement with the experimental ones obtained by planar laser-induced fluorescence (PLIF) method by comparison. Both measured and computed results indicated that the wall-impingement jet would strip off the wall and a secondary space jet was formed when it met with the BUMP on the plane. This resulted in the decrease of the amount of fuel accumulated on the wall. And the area of approximately 1～2 mm thick fuel-rich region between the BUMP and the jet wall-impinging point was extended with the secondary wall-impingement distance increased. The computational results also showed that a "two-vortex structure" which entrained the surrounding air and had an important role in forming lean mixture appeared in the low pressure zone of near the secondary jet. The shape of a BUMP on the plane had significant effects on the formation of a secondary space jet and lean mixture and should be optimized and matched rationally in practical applications.