The invention discloses an LNG vehicle-mounted cylinder and relates to improvement of an LNG cylinder. The LNG vehicle-mounted cylinder comprises an LNG vehicle-mounted cylinder inner container, a pressurizing liquid outlet pipeline, a carburetor, a filling and gas return integrated device and a gas cylinder protective cover, wherein the pressurizing liquid outlet pipeline is arranged on the LNG vehicle-mounted cylinder inner container; the carburetor is connected with the pressurizing liquid outlet pipeline; the filling and gas return integrated device is connected with the LNG vehicle-mounted cylinder inner container; and the gas cylinder protective cover is arranged on the LNG vehicle-mounted cylinder. The LNG vehicle-mounted cylinder is changed integrally and greatly, the over-charging problem and the potential safety hazard are solved, and waste of the LNG is avoided. The space is greatly reduced, the gas cylinder is safer, and the conversion efficiency is improved when liquid fuel is converted into liquid. The LNG is not liable to flow back to the gas cylinder after being gasified in the process of passing through an inner check valve and arriving at an overflow valve. The gas cylinder protective cover is arranged on a shell seal head of the gas cylinder in a detachable mode, so that the protective cover is easy to change when being deformed. . The LNG is not liable to flow back to the gas cylinder after being gasified in the process of passing through the inner check valve and arriving at the overflow valve.