This paper theoretically investigates the characteristics of cavitating bubbles in the pulsed abrasive water jet(PAWJ) and establishes the dynamic equations of cavitating bubbles. The effects of abrasive diameter and density on the spherical bubble collapse are also analyzed. It is found that the change of abrasive diameter rarely affects the bubble collapse when the abrasive diameter and density are small whereas the smaller abrasive greatly blocks the bubble collapse when the abrasive diameter and density are comparably big. It is also shown that when the abrasive density is increased, the fluid viscosity rises, and the kinetic energy of the abrasives near the collapsed bubble is enhanced and meanwhile the intensity of cavitating erosion is weakened.