Gas filling system

The utility model relates to a gas filling system which comprises a low-temperature liquid storage tank, an expansion tank, a buffer tank and a plurality of high-pressure gas cylinders which are sequentially connected through pipelines, the expansion tank is used for expanding and gasifying liquefied gas, and a metering device for controlling liquid outlet flow is connected between the low-temperature liquid storage tank and the expansion tank. The utility model has the beneficial effects that high-pressure gas is obtained by heat absorption gasification of liquid gas in the expansion tank at normal temperature and pressure rise, so that the high-pressure gas can be obtained without power input, the production cost is reduced, the system structure is simplified, and the production efficiency is improved. The mass of the liquid gas entering the filling system is controlled through the metering device, so that the pressure of the gas finally filled into the high-pressure gas cylinder is controlled; and meanwhil