It was published that the water-air two-phase jet could show better impact erosion ability than the common water jet. However, its mechanism remains unproved. This paper tried to investigate the mechanism. Simulation of an air bubble in the water jet impacting on solid surface was carried out. It showed that the bubble burst near the solid surface resulted in pressure pulsation on the solid surface. A test platform was established to compare the pressure pulsations resulted by the water-air jet and water jet impacting on solid surface, respectively. Results validated that impacting pressure pulsation of the water-air jet was higher than that of the water jet, and air bubbles could strengthen the pressure pulsation of water jet impacting on solid surface. An experimental formula of the enhancement factor for the pressure pulsation is obtained.