In view of the problems that the sensor volume is large,and measurement accurac y is low, which exist in the traditional hydraulic detecting system,an embedded nozzle differential p ressure flow sensor based on f iber Bragg g rating (FBG) is researched and designed.Based on the measurement principles of FBG and the differential pressure type flow sensing, the standard nozzle is chosen as the throttling element,and the FBG is pasted on the circular planar diaphra gm with radial direction ,which is used to measure the pressure difference between the two sides of the nozzle when the tested fluid passes through the nozzle. The mathematical relationship between the tested fluid flow and the FBG central reflected wavelength shift is deduced,and the static pressure and dynamic flow characteristics of the sensor are tested by experiment in this paper. According to the test results,the differential pressure sensitivity of the FBG planar diaphragm under the static pressure of the sensor i s 0.712nm/MPa,and the f low sensitivity of the differential pressure FBG flow sensor is 0.067L/s. This sensor has the advantages of high measurement accuracy,small volume and good env ironmental adaptability,and easy to implement multiplex and distributed sens ing network,therefore has a comparative advantage and broad prospects in flow sensing applications.