Clean combustion is critical for marine engines to meet the Tier III emission regulation. In this paper, the effects of EGR and injection strategies (including injection pressure, injection timing as well as multiple injection technology) on the performance and emissions of a 2-stroke, low speed marine diesel engine were investigated by using computational fluid dynamics (CFD) simulations to reach the IMO Tier III NOx emissions target and reduce the fuel consumption rate. Due to the large length scale of the marine engine, RANS simulation was performed in combination with the CTC-SHELL combustion model. Based on the simulation model, the variation of the cylinder pressure curve, the average temperature in the cylinder, the combustion heat release rule and the emission characteristics were studied. The results show that, on the basis of the Tier II-level prototype engine, 25% EGR rate can effectively reduce the NOx emission to the Tier III target, while it also causes the deterioration of fuel consumption rate; Under the fuel injection timing and fuel injection rate constant，increasing the injection pressure can effectively reduce the fuel consumption, and the higher injection pressure will lead to higher average pressure rise rate correspondingly; Pilot‐injection has the potential for simultaneous reductions of NOx emission and fuel consumption，a small proportion of pilot‐injection（5%）with proper injection interval (10°) has the optimal effect. Under 25% EGR rate, the pilot-injection technology combined with the increase of injection pressure and injection timing adjustment can reach the IMO Tier III target while remaining a relatively good fuel consumption rate.