A novel flow sensor based on double fiber Bragg grating was designed and made to overcome the temperature cross-sensitivity problems of traditional single fiber Bragg grating sensor. The elastic umbrella structures were employed as conversion elements and silicone resin as encapsulating material, and an effective solution double-grating structure was taken. The temperature natural compensation and its measuring sensitivity were improved. Finite element was used to optimize the structure of the flow sensor. Its structure and the fluid field around it were simulated and analyzed by ANSYS software within the velocity of 1~20 m/s and the sensitivity of the sensor was calculated. The advantages of silicone resin as encapsulating material and its temperature sensitivity were verified through experiments. The performances of the sensor packaging before and after were tested and the reflection spectrum signal characteristic values of the fiber grating were extracted with good linearity, high response sensitivity of 1.71 nm/kg and 0.103 nm/kg, respectively. The experiment results show that the flow sensor owns simple structure, good linearity and high sensitivity.