The invention relates to a fiber flow velocity sensor, a fiber flow velocity detection device and a fiber used for the sensor. The fiber flow velocity sensor comprises the fiber having a bendable section. The fiber core for transmitting light waves of the fiber is provided with a light leakage hole for enabling a part of the light waves to be leaked at the bendable section of the fiber, and at the place of the same curvature radius when the bendable section bends, the light leakage hole faces to the direction same with the direction of the curvature radius or opposite to the direction of the curvature radius. The fiber flow velocity sensor further comprises a fiber deformation device for enabling the curvature of the bendable section to change correspondingly under the impact of the fluid with the corresponding flow velocity. When the flow velocity of the fluid changes, the bendable section of the fiber changes correspondingly under the action of the fiber deformation device, and the light leakage hole can enable the light intensity of the fiber to change obviously when the bending condition of the fiber changes, thereby realizing improvement of system detection sensitivity, reducing fiber cost, and reducing the cost of matched wavelength processing equipment; production, debugging and maintenance are done conveniently; the system is simple; and the cost is low.