Optical fiber sensors have the advantages of high sensitivity, high-inherent insulation, and good anti-electromagnetic interference ability compared to standard monitoring technologies. However, humidity sensors based on fiber Bragg gratings are easily affected by temperature and stress, resulting in issues such as significant humidity measurement errors and low stability. This paper proposes a fabrication method based on a single grating half-coated temperature and humidity sensor to solve these problems. First, a moisture-sensitive material is coated on half of the grating, and the other half is a bare grating area. Then, the bare grating reflection spectrum peak curve is then Gaussian fitted to establish the functional relationship between ambient temperature and center wavelength λ. Finally, the relationship between the area S enclosed by the grating reflection spectrum curve and the peak power under various environmental humidity conditions is analyzed. The function model of the area S and the relative humidity of the environment is established. The sensor is tested by a temperature and humidity generator. The experimental result shows that the sensor has good repeatability in the range of 10%‒90%RH (%RH is relative humidity). The humidity monitoring sensitivity is 2.95/%RH, and the response time is 6.6 min, which matches the temperature and humidity monitoring requirements in storage and other fields while also providing a new solution for temperature and humidity monitoring in related fields.