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A transparent nozzle was designed to replace the sac and orifice of the original injector. Visualization experimental apparatus with a long distance microscope together with an ultrahigh speed CCD camera was employed to study the cavitation characteristic in the nozzle and the initial spray structure in the near nozzle region by photography technique with the help of backlighting. High spatial and temporal resolutions allowed a detailed observation of the very emergence of fuel from the nozzle orifice to the outside of nozzle. The experimental results showed that the residual fuel and initial bubbles were trapped in the injector hole after the end of injection, which had an important effect on the initial spray structure of the next injection. The cavitation was related to the needle lift and the injection pressure, and it was found that higher injection pressure led to earlier cavitation inception. Moreover, the types of free cavitation, cloud cavitation and string cavitation were also observed. In addition, based on the large eddy simulation (LES) and volume of fluid (VOF) multiphase flow model, the evolution of the initial bubble in the injection hole and the formation of the initial spray structure were simulated. The computational domain and settings mimicked the experimental injector internal geometry and experimental operating conditions. The initial bubbles inside the injector influenced the spray structure and could be a source of the observed deviation between experimental and numerical results. But the experimental results were basically consistent with the simulation results.