Abstract: A simulation was carried out based on the coupling of chemical kinetics and computational fluid dynamics（CFD） to investigate the characteristics of combustion and emissions of ammonia-diesel dual fuel low-speed engine. The mechanism of ammonia-diesel dual fuel was proposed and it could predict well with experiment results including ignition delays,laminar flame speeds and important species concentrations. Then,in CONVERGE,a three-dimensional CFD model of a low-speed marine engine was established,and empirical parameters of the ammonia laminar flame speed in the G-equation model were determined. Finally,the influence of compression ratio and equivalence ratio on the ammonia-diesel dual fuel combustion process was studied. The results show that the stability of ammonia ignition combustion can be improved by appropriately increasing the compression ratio. When the compression ratio is 14.5,higher efficiency can be obtained and peak combustion pressure can be controlled within a reasonable range. When the equivalence ratio is around 0.410,the performance is optimal. A higher equivalence ratio will cause the ignition to advance too early and the combustion temperature will increase significantly,resulting in a decrease in thermal efficiency and a significant increase in NO_x,while a lower equivalence ratio will result in a decrease in the indicated thermal efficiency. The comprehensive results show that when the equivalence ratio is 0.410 and the compression ratio is 14.5,the optimal values under the coordination of efficiency and emission can be obtained.