Abstract: In order to explore the mechanism of highspeed diesel engine combustion system parameters on the combustion properties, the matching laws between fuel injection system parameters and combustion chamber structures in high speed direct injection (HSDI) diesel engine was studied by using threedimensional CFD numerical simulation method. The spatial distribution of fuel vapour and characteristics of fuel /air mixing were analyzed. In order to quantitatively describe the performance of fuel/air mixing, the parameters about the rate of turbulent mixing and concentration variance of mixture were established. Moreover, weight analysis of the effect of fuel injection system and combustion chamber structural parameters on indicated power was carried out using orthogonal method.The results show that diesel engine power decreases after increasing with the increase of chamber caliberdepth ratio. When the caliberdepth ratio equals to 6.4, diesel engine is the most powerful, mixing is the most uniform. For different combustion chamber, fuel injection system parameters are of different weights for power. With the combustion chamber caliberdepth ratio increases, the weight of injection pressure decreases, the weight of spray angle of increases, the weight of nozzle number and diameter reduces, the weight of injection timing decreases and then increases.