A novel flowrate sensor based on a couple of fiber Bragg gratings( FBGs) has been proposed, consisting of fiber grating pressure sensing setup and Venturi tube. The expression of relationship between the flowrate and the wavelength shift difference of the FBGs is derived. The pressure that two sides of the cross section of the aluminum foil tube in the pressure sensing setup results in the distortion of an isosceles triangle cantilever structure. The distortion results in the wavelength shift of a couple of FBGs that are mounted at either side of the cantilever. By monitoring the wavelength shift difference of the two FBGs, the flowrate can be obtained. The cross-sensitive problem of the FBGs sensor can be solved by compensating the temperature effect. The preliminary experiments have been carried out, and the results verify the feasibility of the proposed sensor with a measurement range from 8 to 200 mm/s.