The gas meter has the function of prepayment. The user gives the gas fee to the management department. The management department writes the amount of gas purchased into the IC card. The user inputs the information in the IC card into the gas meter, and the gas meter opens the valve to supply gas. In the process of users'gas consumption, the amount of gas meter is automatically checked by micro-computer, and the purchased amount is exhausted. The gas meter automatically closes the valve and stops supplying gas. Users need to buy gas again before they can open the valve again.