In order to improve the ambient humidity sensitivity of fiber Bragg grating (FBG), coating graphene oxide (GO) polyvinyl alcohol (PVA) solution on FBG for humidity sensitization is proposed in the paper. Firstly, the humidity response of the sensor is studied theoretically, and the sensor samples are fabricated by pulling coating method, then the influence of the humidity sensitive solution mixture ratio and the film thickness on the humidity sensitivity is discussed experimentally. Further experimental results show that when the mixture ratio of graphene oxide-polyvinyl alcohol is 9∶1 and the coating thickness is 89 μm, the humidity sensitivity of the sensor is 2.3 pm/%RH (relative humidty) in the humidity range of 50%—60%RH. The humidity sensitivity of the sensor is 7.7 pm/%RH in the humidity range of 60%—70%RH. The humidity sensitivity is 47.2 pm /%RH in the humidity range of 70%—80%RH. The teumperature sensitivity is 13.2 pm/℃, humidity measurement instability is 0.064 7%RH, and response and recovery time is 0.84 s and 11.46 s, respectively. The sensor has advantages of simple manufacture, high humidity sensitivity and good stability, which makes it has great application potential.