In order to study the influence of parameter optimization of the fuel injection system on the performance of diesel engine, the fuel injection system’s model was built by using AMESim code, and the related structural parameters were optimized by using orthogonal experimental design method. The optimized fuel injection law was led into the high pressure cycle model for combustion calculation by coupling AMESim and AVL_FIRE software, then the fuel injection system’s parameters were optimized. Simulation results show that the designed pressure can be met when the fuel injection parameters are 15 mm-0.22 mm-0.46 mm·(CaA)^-1 and 14 mm-0.30 mm-0.46 mm·(CaA)^-1(diameter of plunger-diameter of orifice-cam velocity ). The fuel consumption rate is reduced by about 3.8% and 5.4% compared with the original machine respectively, but the NO _xemissions are increased by approximately 98.2% and 144.4% respectively. After re-optimization, the fuel consumption rate is reduced by about 10.5% compared with the original machine under the optimal combination of parameters to reduce fuel consumption optimization target.The NO_xemission is reduced by about 45.3% to reduce NO_x emission optimization target.