Based on Taguchi design, a turbocharged diesel engine was numerically simulated by CONVERGE software, and the synergistic effect of the number and the diameter of injection holes and the injection pressure on the performance of diesel engine was explored. The results show that the incylinder pressure rise rate is obviously large and the sharp rise timing advances under the conditions of high injection pressure or large crosssectional area of injection hole, which is not conducive to the smooth operation of diesel engine. Properly increasing the injection pressure, increasing the number of injection holes and decreasing the diameter of injection hole can promote the fuel atomization mixing, accelerate the combustion of incylinder mixture, improve the engine power performance and economy, and reduce NO_x and soot emissions. For the fuel consumption rate and NO_x emission, the number of injection holes is the most sensitive, followed by the diameter of injection holes and injection pressure. For the soot emission, the influencing degree from high to low is the injection pressure, the number of injection holes, and the diameter of injection holes by order. By synergistic optimization of injection pressure and injection hole parameters, the fuel consumption rate, NO_x and soot generation reduce by 4.37 g/(kW·h), 11.2% and 9.14% respectively, compared with the original engine.