A humidity sensor is proposed by coating aluminum oxide and polyvinyl alcohol film on the etched fiber Bragg grating by pulling technique. The strain generated by the hydro-philicity of the humidity sensitive film induces the central wavelength of fiber Bragg grating shifting, thus the environmental humidity monitoring is realized. In the experiment, the diameter of fiber Bragg grating is etched to 50 μm by hydrofluoric acid, the mixture ratio of aluminum oxide and polyvinyl alcohol solution is 9:1 and the coating thickness of humidity sensitive film is 80 μm. The experimental results show that the humidity sensitivity is 6 pm/% RH in the humidity range of 40% RH-58% RH, the humidity sensitivity is 32.3 pm/% RH in the humidity range of 58% RH-70% RH, the temperature sensitivity of the sensor is 14.2 pm/°C in the temperature range of 25~70 °C. The instability of the sensor is 0.0745% RH, and the human breathing testing shows that the response time and recovery time of the sensor are 1.94 s and 5.19 s, respectively. The sensor has advantages of simple fabrication, high humidity sensitivity, good stability, which indicates it has application potential.