Piston bowl geometry has important effects on diesel engine combustion. Especially for a high power density engine, much more fuel requires to burn across the cylinder in a short period after the top dead centre (TDC). Therefore the piston bowl geometry plays a critical role for the air/fuel mixing process and the combustion process. In this paper, a 3-D in-cylinder combustion modeling was carried out for a high power density engine. The ω type of bowl shape was described by seven independent parameters. Five of them are conducted to investigate their effects on the combustion process. The results show that the bowl diameter has significant effects on combustion both in the pre-mixing combustion period and in the diffusion combustion period. There exists an optimized bowl diameter value to obtain a highest indicated power. The re-entrant angle has an important effect on pre-mixing combustion and there also exists an optimized value to reach a highest indicated power. The bottom concave arc radius has significant effects on premixing combustion but has little effects on the diffusion combustion. The smaller concave arc radius gives higher indicated power. The central depth and the bottom convex arc radius have noticeable effects on pre-mixing combustion, but have little effects on the diffusion combustion.