<p>This study is to reveal the influence of main shape parameters of stepped combustion chamber on the combustion process, and to establish a parameterized design method for the combustion chamber that matches the fuel injection system. Based on the CFD software CONVERGE, the effects of important combustion chamber shape parameters and injector parameters on the fuel distribution, combustion process, and thermal efficiency in the cylinder were studied. The results show that among the shape parameters of the combustion chamber, lip offset angle (LOA) has the greatest impact on fuel distribution. For one certain injection angle, using an appropriate LOA can control the ratio of fuel in the upper region and lower region at a best value, thereby accelerating mixing, improving combustion rate and thermal efficiency; for different injectors, using combustion chambers with large volume of the upper region and appropriate LOA, combined with a large injector aperture and large injection angle, can achieve the most significant improvement in thermal efficiency. Based on these conclusions, the combustion system of a heavy-duty diesel engine was optimized, and the experimental results show that its maximum indicated thermal efficiency has increased by 0.6% absolute compared to the base combustion system.</p>