The nozzle flow and cavitation of diesel engine nozzle directly affected the fuel injection and atomization, which affected the performance and emissions of diesel engine. Taking two asymmetric nozzles of minisac and VCO as examples, the influences of entrance pressure and back pressure on mass flow rate were researched through the simulation of cavitation and flow with Fluent software. The results show that the flow of each orifice for minisac nozzle is larger than that for VCO nozzle. VCO nozzle is easier to produce cavitation at low and medium pressure，but the probability to generate cavitation for both types of nozzles is nearly the same at high pressure. The mass flow is linear to pressure difference with the decrease of outlet pressure at constant inlet pressure when the cavitation doesnot occur, increases continually when the cavitation happens and keeps unchanged when the super cavitation happens. In addition, the mass flow becomes small and the cavitation becomes sensitive with the increase of axial included angle. For the two types of nozzles, the cavitation of orifice happens mainly at upper part except that that the cavitation of third and fourth orifice for minisac nozzle happens at upper and lower part.