The invention provides an uncompressed stroke internal-combustion engine with independent gas supply, comprising a main body, an input unit, an output unit and an exhaust unit. The main body is provided with at least one cylinder; the input unit is connected with the cylinder and used for inputting high-pressure fuel to the cylinder and enabling the cylinder to have set pressure inside; the output unit is connected with the cylinder and used for outputting power generated by combusting the high-pressure fuel; and the exhaust unit is connected with the cylinder and used for exhausting waste gas generated after the high-pressure fuel is combusted. The invention directly enables the cylinder to have the set pressure inside by directly inputting the high-pressure fuel to the cylinder and then carries out a combustion stroke, has smoother operation of an engine because the uncompressed stroke internal-combustion engine only needs to carry out a combustion and exhaust stroke at each output time, and can increase the rotating speed of the engine to very high rotating speed.