A DNS study which employs VOF method is presented to investigate the collapse of cavitation bubbles near a rigid wall. The motion of bubbles is driven by the pressure difference between the interfaces of bubbles. We analyze the evolution of bubble deformation, pressure distribution and the impact received on the wall. The results shows that the bubbles far from the rigid wall collapse first, while other bubbles appear to collapse toward the wall subsequently. When the last bubble disappears, the impact received on the wall reaches a maximum value. Compared to the single bubble, multiple bubbles can generate greater degree of impact on the wall.