The inner surface structure of nozzle has great influence on the internal flow characteristics, and then affects the cavitation characteristics of the nozzle. The structure model of the organ pipe nozzle outlet section was selected, and the inner surface bulge structure was established. The flow field of the rough pipe was analyzed by FLUENT, and the pressure variation curve of the near wall flow field was obtained. Then, the probably pressure variation function of the flow field was fitted by MATLAB. At last, the evolution of cavitation in the flow field was studied based on the bubble dynamics equation. The results show that the presence of the bulge has a significant influence on the near wall flow pressure, when the bulge reaches a certain amount, the pressure fluctuation shows a similar alternating change; the increase of height and width of the bulge increases the rate of cavity growth, in the beginning of bubble evolution; as time goes on, the increase in the size of the bulge accelerates the collapse of the bubble.