Provided is a water-jet propulsor utilizing engine exhaust. The water-jet propulsor comprises a guide pipe internally provided with a rotary shaft, a guide vane wheel and a rear guide vane body are arranged on the rotary shaft, and a water inlet grid is arranged at the front end of the guide pipe; the rotary shaft is further provided with a front guide vane body located between the water inlet grid and the guide vane wheel, a prewhirl guide wheel composed of a prewhirl guide pipe and prewhirl vanes is arranged outside the water inlet grid, and the whirl direction of the prewhirl vanes is identical to those of the front guide vane body, the guide vane wheel and the rear guide vane body; a gas delivery pipe is connected to the water inlet grid and a gas discharge pipe of an engine of a shipbody, and a check valve is arranged on the gas delivery pipe. By the adoption of the technical scheme, water flow is pressurized through the high-temperature and high-pressure exhaust generated by theengine, and thus high-speed water jet is generated; meanwhile, the check valve is arranged on the gas delivery pipe, water backflow is avoided, combustion waste gas is made full use of, and the propulsion efficiency is improved.