According to the actual experimental condition and theoretical analysis, a finite element model was established to describe the surface modification process of scanning electron beam of 6A02 aluminum alloy. The phase change process and thermal radiation were considered in the simulation. The temperature simulation revealed the ultrahigh rate of the heating and cooling, rapid melting and re-solidification within seconds in the range of millimeters in depth. The calculated melting zone was an irregular semicircle, the x-axis length was about 2.9mm, and the axial depth was about 1.4mm. This research will predict the melting condition.