Gear flow transmitter belongs to a kind of volumetric flow transmitter and can be used for measuring volume and flow precisely. The flowing medium makes the gear engage and rotate. Under the flowing effect of fluid, pressure difference is formed between the inlet and outlet of instrument. One pair of gears can rotate freely without the need of power supply. The empty cavity between gears is filled with liquid, which is discharged through rotation. The liquid flowing through instrument and liquid flow can be known through measuring the number of revolutions of gear.