This paper presents the simulation results of histories of pressure, temperature and NO concentrations as well as combustion process and NOx formation in a marine diesel engine. The simulation was done within a full engine cycle with a three-dimensional, transient combustion model including a more accurate NO formation model. Simulation results were verified by data obtained from benchmark tests and further analyses of distributions of pollutants were carried out in this paper. Conclusions from simulation about engine combustion and NOx formation have been finally achieved.