A new coupled fiber optic humidity sensor based on a double-tapered fiber twisted weakly coupled structure coated with a graphene oxide/polyvinyl alcohol (GO/PVA) film has been reported for the first time, to the best of our knowledge. The sensor adopts a 2×2 coupler structure with a waist diameter of 20 µm. The GO/PVA composite film is coated in the weakly coupled area to increase the sensitivity of the sensor. The thickness of the coating layer is about 3 µm. The sensor can realize linear sensing in the relative humidity (RH) range of 45%-85%RH with a dynamic response time of 1.9 s and a recovery time of 5.7 s. The sensitivity of the sensor is up to 0.002/%RH, and the linearity of the sensor is as high as 98.65%. Moreover, the sensor has good stability, reversibility, and low-temperature crosstalk.