The internal flow and cavitation phenomenon in diesel injector nozzles play an important role in mixture formation,which is decisive for combustion efficiency and pollutant formation.In this paper,Large Eddy Simulation(LES)method has been used for modeling cavitation in a simple contraction nozzle of conventional diesel and biodiesel(soybean oil).Considering that sensitive areas of the flow inside the nozzle were different,varying grid density technology was used in meshing the geometry model.In addition,the code has been verified by Winklhofers test case in terms of mass flow at the outlet,together with the internal pressure distribution.Aimed at the trend of high injection pressure,different injection pressure(160MPa,80MPa)and constant backpressure(5MPa)were investigated.From research results,four important conclusions can be drawn.Firstly,compared with the diesel fuels,the mass flow rate is always higher and the effective velocity is smaller for biodiesel,nevertheless,the diesel fuel cavitates more than biodiesel for the same pressure conditions.Secondly,the mass flow rate increased with the increase of the pressure difference under the same injection pressure,but after reaching the critical cavitation point,the mass flow rate became constant.Thirdly,in comparison with biodiesel,the mass flow collapse was reached earlier for diesel.Hence,the biodiesel can inhibit cavitation.Fourthly,increasing the injection pressure can enhance the cavitation intensity for both fuels.