An experimental system of flow visualization was setup based on a transparent scaledup vertical injector nozzle tip. Based on the similarity principle of hydrodynamics, the generation and development of cavitation flow and its effect on spray were investigated and the influences of injection pressure and needle valve lift on cavitation flow were analyzed with a high resolution and speed CCD camera under the injection pressure of 0.15 MPa-1.70 MPa, the back pressure of 0.1 MPa and the ambient temperature of 20 ℃. The experimental results show that the cavitation flow in the nozzle is unstable with the film cavitation and string cavitation. The strength range of film cavitation and string cavitation will increase with the increase of injection pressure and needle valve lift. Both the film cavitation and the string cavitation will increase the spray cone angle. In addition, the symmetry of string cavitation spray is better than that of the film cavitation spray.