The invention provides a purely-mechanical aircraft carrier engine prime motor with compressed air as a power source in order to overcome existing backward technologies of aircraft carrier diesel engines and avoid undetermined potential safety hazards and poor safety of high-energy-consumption reactors where nuclear fuel is combusted. An advanced air compression technology is adopted, the compressed air directly acts on machines, a plurality of air cylinders are formed on a mechanical system, potential energy is converted to kinetic energy by the compressed air in the air cylinders through basic principles and ingenious technologies, the kinetic energy acts on a mechanical arm and is transmitted to a mechanical shaft in a mechanical transforming mode to make the shaft rotate at a high speed and generate large torque, the compressed air completely does work in the air cylinders without being wasted, and all the potential energy is converted to the kinetic energy. The aircraft carrier engine prime motor saves energy, is efficient, simple in structure, easy and convenient to machine, small in noise and convenient to maintain.