Marine combustion piston engines are more often equipped with common rail systems, which provide multi-part injection fuel delivery to the cylinder. Dose selection must take into account, among others, its duration, the engine speed and load torque. Practical use of a specific fuel dosing is usually preceded by a study on the test stand simulating the injection process and its dependence on the dose parameters. The authors have presented a method for the selection of these parameters in the case of one-and two-part injection in the medium speed marine engine. There has been presented the manner of creating a mathematical model of the fuel dosing during the injection and research of its characteristics in order to optimize the selection of the amount of fuel, that can be applied in the design of the CR system in the marine combustion engines.