Disclosed is an optical fiber flow velocity measuring apparatus and method integrating high and low ranges. The apparatus includes an integrated optical fiber flow velocity sensor, the integrated optical fiber flow velocity sensor includes a sensor body; a fluid channel, a fluid through hole, a full-pressure channel, a static-pressure channel, a low-pressure chamber and a high-pressure chamber are provided inside the sensor body; a first optical fiber sensing element is provided between the low-pressure chamber and the high-pressure chamber; a second optical fiber sensing element is provided in the fluid through hole and is perpendicular to a flow direction of a fluid to be measured; the first optical fiber sensing element and the second optical fiber sensing element are sequentially connected in series through a single-mode optical fiber; both ends of the single-mode optical fiber are connected into a wavelength division multiplexer; a pump light source is connected with the wavelength division multiplexer through a common optical fiber; an optical fiber grating demodulator is connected with the wavelength division multiplexer through a common optical fiber; and a flow velocity arithmetic unit is electrically connected with a optical fiber grating demodulator. It's an object of the present disclosure to solve the problems that the electric circuit is too complicated and that it is not easy to integrate in one apparatus when flow velocity conversion devices based on different principles are integrated.