Cavitation is an important multiphase phenomenon that occurs frequently in the nozzle internal flows.The structure of injector nozzle directly influences the inner flow characteristics,which cause great effect on the spray jet atomization at nozzle exit.In this study,a single-hole x-ray CT scanned nozzle model was obtained and then utilized to generate the simulation grids directly.Based on that,the three-dimensional simulation investigation on the nozzle internal flow was conducted to unveil the dependence of the orifice structure on the inception of in-nozzle cavitation.Results show that: Because of the more accurate geometry information contained in the 3D simulation,the flow characteristics and the cavitation phenomenon are uneven in the azimuthal direction of the orifice.The orifice inlet rounding radius has a great effect on the flow field near the orifice inlet region.The influence becomes stronger when the flow is closer to the orifice wall.A dimensionless parameter is proposed to estimate the inception of the in-nozzle cavitation.Enlarging the orifice inlet rounding radius can effectively reduce the vapor fraction inside the nozzle.A critical orifice inlet rounding radius has been put forward to predict the inception of the cavitation inside the nozzle.