A three-dimensional simulation model of the TCD combustion system of a six cylinder diesel engine for a generator set was established based on AVL Fire software, and the simulation model was validated by using experimental results. Then the optimization for the TCD geometries of combustion chamber and the matching of  spray angle were conducted. By using sensitivity analysis method, the influence degree of main chamber geometries such as combustion chamber diameter and lower chamber outlet diameter on the combustion performance of TCD combustion system was obtained based on the evaluation index of indicated power. According to the influence degree, each geometry was optimized in descending order and the spray angle was matched simutaneously. Accordingly, the indicated power of single cylinder increased by 0.79 kW, and the combustion performance of the six cylinder diesel engine improved under power generation conditions. By analyzing the distribution of cylinder fuel/air equivalence ratio under different combustion chamber geometries, it was found that the cylinder air utilization rate improved, the distribution of equivalence ratio became more uniform, and the fuel/air mixed much better after matching the optimal parameters. Therefore, the TCD combustion system showed better combustion performance.