Abstract: In order to study the cavitation fuel flow characteristics inside the diesel nozzle, based on the same cavitation number and the similar structure of the baseline nozzle, the flow characteristics of the nozzle were tested on the optical test rig, together with the CFD three-dimensional simulation. An investigation on the characteristics at the nozzle outlet during the cavitation period, and the influence of cavitation on the flow characteristics such as the velocity, the density, and the turbulence kinetic energy were presented. The flow characteristics at the nozzle outlet were analyzed as the back pressure decreased. The results show that for stable inlet pressure, cavitation at inlet cross-section becomes first stronger and then stable as the back pressure drops. At the nozzle outlet, the cavitation and the fuel density continue increasing with the decrease in the back pressure. The turbulent kinetic energy constantly increases with back pressure decreasing in the nozzle. However, the cavitation increase rate at saturation stage is less than that of without cavitation and cavitation developing period. During the no cavitation stage, the liquid average velocity has no difference at the inlet and outlet cross-section of nozzle, but the velocity difference between the nozzle inlet and the outlet increases during both the cavitation developing and saturation periods.