In order to achieve stable and accurate detection of methanol vapor concentration, a fiber Bragg grating (FBG) methanol sensor based on polymethyl methacrylate (PMMA) film was proposed. First, use hydrofluoric acid to etch part of the cladding layer, and coat a layer of PMMA film on the surface of the gate region. Then, a measurement system was constructed, and a theoretical model for the sensor to detect methanol vapor was established. Finally, a temperature compensation unit is introduced to eliminate the effect of temperature on the measurement of methanol vapor concentration. The effects of PMMA film thickness and temperature and humidity on the sensitivity of the sensor were experimentally studied, and the response time, selection sensitivity and detection limit of the sensor were tested. The results show that there is a linear relationship(R2=0.992) between the center wavelength drift of the sensor and the concentration in the methanol concentration range of 20-160 mg/L. In the temperature range of 20-40 ℃ and relative humidity of 40%-80%, the sensor can accurately detect the change of methanol vapor concentration with a sensitivity of 0.292 pm/(mg·L-1), a relative error of 9.3%, and a lower detection limit of 20 mg/L.