The invention provides an internal combustion engine cooling method, which is characterized in that a cooling agent spray nozzle is arranged on a cylinder cover of an internal combustion engine; a cooling agent is directly sprayed into an air cylinder of the internal combustion engine to be cooled; a cylinder body of the engine is lengthened, so that the stroke of the piston is lengthened. The spraying-in frequency of the cooling agent is completely identical to the ignition frequency of a spark plug; only the time is properly delayed; the spraying-in quantity of the cooling agent is preciselycontrolled by a computer so that the temperature of the cylinder body is precisely controlled; after the fuel is combusted to complete the work application, the cooling agent is sprayed; the coolingagent expands and evaporates in the cylinder body when meeting high temperature; the cooling agent steam pushes the piston to continuous apply the work.