The invention relates to a propulsion and dynamic system for large ocean vessels, in particular to a propulsion system for large ocean vessels. The system comprises a large turbocharging multi-cylinder two-stroke crosshead type diesel engine which serves as the primary motive power and is coupled to a propeller shaft, and one or a plurality of much smaller diesel engines which serve as the secondary motive power and are coupled to electric generators. The primary engine needs to be started and operated by electric power, hydraulic power and aerodynamic force. The primary engine needs heating power and a little hydraulic power in the short cessation process, and needs hydraulic power, aerodynamic force and electric power in the starting process. According to the invention, when the primary engine ceases, starts and operates, a power unit providing hydraulic power is driven by an electromotor which obtains power from the electric generator driven by the smaller diesel engine.