The three-dimensional numerical simulation of gas-liquid two-phase flow in diesel nozzle with convergent conical orifice（CDN）was carried out by using the mixed multiphase cavitation flow model, and the effects of injection pressure, injection back pressure and needle valve movement on the cavitating distribution, the turbulent kinetic energy distribution, the mean flow velocity at outlet(MFVO) and the discharge coefficient were analysed. The results show that the increasing in the injection pressure or the needle valve`s open velocity will enhance the cavitation effect, strengthen the flow disturbance, improve MFVO and the cycle fuel injection quantity, which are beneficial to the performance of diesel engine, the fuel injection and atomization; with the increase of the injection back pressure, the discharge coefficient of CDN is increased slightly, but the cavitation effect, the flow disturbance and MFVO are decreased gradually; under the same injection condition or needle valve lift, the cavitation effect of CDN is weaker than that of diesel nozzle with cylindrical orifice, MFVO and the discharge coefficient of CDN are higher than those of diesel nozzle with cylindrical orifice.