A visualization unit with a proportion of the multi-hole injector nozzle for cavitating flow was developed, and by means of high-speed video camera, the pictures of the cavitating flow in a large-scale transparent nozzle were taken under various injection pressures. A three-dimensional grid model of the injector nozzles was established, and the three-dimensional numerical simulation of cavitating flow in nozzle holes of a multi-hole injector combined with these pictures from experiment was utilized to analyze flow characteristics of single-phase flow to supercavitation flow. The relationship between injection pressure, non-dimensional cavitation parameters and the discharge coefficient, as well as the critical conditions when the cavitation appeared was pointed out clearly.