System and method for measuring flow rate of fuel gas online

The invention creatively applies to online measuring of flow rate of fuel gas. A system and a method for measuring the flow rate of the fuel gas online can be used as reliable means for comparing flow rate of different test stands or a turbine flow meter and a fuel gas calibration method for calibrating online. With the adoption of the measurement method, a confidence coefficient of acquired data can be increased. The system for measuring the flow rate of the fuel gas online is that a measuring cylinder is mounted on a movable stand; the measuring cylinder comprises a barrel, a measuring cylinder body, a piston, a piston rod and limiting devices; the piston is positioned in the measuring cylinder body and divides the measuring cylinder body into a left cavity and a right cavity; an oil inlet and an oil outlet are respectively formed in the left cavity and the right cavity; pneumatic ball valves are mounted on fuel pipelines of the oil inlet and the oil outlet; two ends of the piston rod extend out from the measuring cylinder body, and the end equipped with a grating indication probe is positioned on a grating; the limiting devices for limiting the piston in moving are mounted at two inner ends of the measuring cylinder; a measuring and control system is used for measuring and calculating the grating indication probe as well as turning on and off the pneumatic ball valves.