The phase transformation and the structure change of the silicon surface are investigated by molecular dynamics simulation of the incidence and recoil of a nanoparticle at the monocrystlline silicon surface. The simulation shows that during the collision process, the impacted region on the silicon surface transforms from diamond structure to a molten state, then goes through the state of supercooled liquid, and finally solidifies into an amorphous phase. Furthermore, the temperature of solidification transformation calculated from the simulation is very close to the glass transition temperature of silicon. The structure changes taking place during the nanoparticles recoiling process are also revealed. Beginning with an instantaneous, highly disordered, and badly depressed supercooled state, the impacted region evolves along the direction to a more ordered and lessdepressed state. These evolutional tendencies are determined by the cooling andunloading process the impacted region undergoes. The amorphous silicon formed after the collision has the average coordination of 5.27, and the fivefold and sixfold coordinated atoms accounts for 61.5% of the whole atoms in the impacted region.