NOVELTY - Device comprises a medium-pressure CNG (compressed natural gas) tanker, a natural gas buffer tank, a natural gas storage tank, a raw gas buffer tank, a fuel gas buffer tank and a connecting pipeline valve system. The valve system comprises three cut-off valves and a regulating valve. The CNG tanker is respectively connected with the natural gas buffer tank and natural gas storage tank through the two cut-off valves. A middle upper outlet of the natural gas buffer tank is connected with a lower inlet of the raw gas buffer tank through the one cut-off valve.    USE - The device is useful for converting medium pressure of fuel gas into low pressure in natural gas pyrolysis hydrogen production (claimed).    ADVANTAGE - The device: has simple structure; is simple to operate; can enable the consumption of the medium-pressure CNG tanker to achieve the maximum limit; enhances the application efficiency; lowers the cost. The method: can save the transportation cost by 10%; and can provide safe and stable low-pressure fuel.    DETAILED DESCRIPTION - Device comprises a medium-pressure CNG (compressed natural gas) tanker, a natural gas buffer tank, a natural gas storage tank, a raw gas buffer tank, a fuel gas buffer tank and a connecting pipeline valve system. The valve system comprises three cut-off valves and a regulating valve. The CNG tanker is respectively connected with the natural gas buffer tank and natural gas storage tank through the two cut-off valves. A middle upper outlet of the natural gas buffer tank is connected with a lower inlet of the raw gas buffer tank through the one cut-off valve and a middle upper outlet of the natural gas storage tank is connected with an inlet of the fuel gas buffer tank through the regulating valve. An INDEPENDENT CLAIM is also included for converting medium pressure of fuel gas into low pressure in natural gas pyrolysis hydrogen production, comprising (a) converting medium pressure natural gas to produce hydrogen production raw material gas: conveying natural gas of medium-pressure CNG tanker into a natural gas buffer tank connected to hose pipe through a pipeline, maintaining pressure to 2-2.1 MPa, conveying the natural gas of the natural gas buffer tank into a feeding gas buffer tank through the cut-off valve, maintaining the pressure to 1.9 MPa, conveying the natural gas in the feed gas buffer tank into the hydrogen pyrolysis system, and maintaining stable reaction pressure at 1.65-1.75 Mpa; (ii) maintaining natural gas initial pressure in the medium-pressure tube beam container to 3.9 MPa, connecting the hose pipe with the gas buffer tank through the pipeline, conveying the natural gas until pressure in the natural gas buffer tank is dropped to 2.1 MPa, closing the conveying of the natural gas from the natural gas buffer tank through the cut-off valve, opening the cut-off valve to convey into the natural gas storage tank, pressurizing 1.9 Mpa pressure into the medium-pressure CNG tanker, closing the stop-valve, filling gas into the medium-pressure CNG tanker through a gas filling station, and extracting 10% natural gas feedstock gas from the natural gas medium pressure car; and (iii) low pressure fuel gas system: conveying the natural gas in the natural gas storage tank into fuel gas buffer tank through the regulating valve, maintaining 0.2 Mpa pressure in the fuel gas buffer tank, combusting to exchange heat under pressurized state, supply the heat, and allowing the system to achieve stable low-pressure fuel gas.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the device for converting medium pressure of fuel gas into low pressure in natural gas pyrolysis hydrogen production.