Objective In modern production life, there is an important and widespread need to achieve accurate measurement of temperature and relative humidity. Conventional capacitive moisture-sensitive elements lack stability, interactivity and corrosion resistance, and can monitor a small range of humidity. Not only does the characteristic response drift severely in long-term use, but also the accuracy is insufficient to meet the needs of the finishing industry.In contrast, fiber optic sensors have the unique advantages of small size, light weight, anti-electromagnetic interference corrosion resistance, etc. And fiber optic gratings are sensitive to changes in external influences such as temperature and pressure, and are therefore used in large numbers in the sensing field. Based on this, the SPR effect has been widely noticed for its advantage of improving the sensitivity of optical fibers to changes in refractive index of the surrounding environment. In recent years, researchers have developed various temperature and humidity sensors based on the SPR effect and fiber grating using this principle. However, the sensitivity of these sensors needs to be improved, and often cannot achieve simultaneous measurement of temperature and humidity. We propose an SPR-based temperature and humidity sensing structure for single-mode optical fiber grating, which is coated with silver nanofilm after etched cladding, and then coated with a moisture-sensitive film. The structure uses PVA as the moisture-sensitive material combined with SPR effect for humidity detection, and uses fiber grating as the temperature-sensitive device to achieve the measurement of temperature and humidity changes in the surrounding environment.Methods The coated fiber was first removed from the grating side of the fiber with a length of about 10 mm. Then HF acid solution with a concentration of 37.6% was applied dropwise to the surface of the removed fiber, and the corrosion condition was observed several times using an optical microscope until the corrosion cladding diameter was 16m. The treated fiber was fixed on a slide and plated with a silver film of 40 nm thickness by a magnetron sputtering coater. At the end of the silver plating process, the fiber optic sensing structure was flipped to the back side and the plating process was repeated to ensure uniform coating of the entire fiber optic sensing structure. Next, add 0.5 g of PVA powder to a small beaker, add deionized water to a total weight of 10 g, place it on a baking table and heat it to 60℃. Stir while heating until the PVA is completely dissolved, then apply the prepared wet-sensitive solution onto the slide evenly. After submerging the silver-plated part of the fiber in the wet-sensitive solution, the fiber is slowly and steadily lifted out. And as the solvent evaporates, the PVA solution attached to the surface condenses and forms a thin film.Results and Discussions The sensing structure has a good response in temperature and humidity sensing. Both the SPR resonance peak and the central reflection peak were significantly shifted when the temperature and humidity were changed. In thehumidity experiment, Figure 6 shows the resonance peak shift in the transmission spectrum corresponding to the sample under humidity conditions varying from 30%RH to 80%RH. As the humidity increases, the spectral resonance peak shifts unidirectionally toward the short wavelength and the depth of the valley gradually increases. The crosstalk effect of temperature on humidity is shown in Figure 7, and the temperature sensitivity of PVA can be analyzed by linear correction using Formula 4. In the temperature experiment, the fiber grating temperature response, the external temperature increases from 20℃ to 70℃, and the fiber grating center reflection wavelength shift and temperature change is a good linear relationship, as shown in Figure 8. And the experimental results show that the ambient humidity change does not cause a crosstalk effect on temperature detection.Conclusions In this paper, we propose a new fiber grating temperature and humidity sensor based on SPR effect. By cladding etching, the fiber core light is coupled into the cladding, and a 40 nm thickness silver nanofilm is coated outside the cladding, so that the light coupled into the cladding and the silver film excite the SPR effect. The fiber grating is shifted with temperature changes affecting the center reflection wavelength. It has high linearity for temperature measurement, while the silver nanofilm is coated with a moderate thickness of PVA moisture-sensitive film, using the characteristics of the refractive index of the moisture-sensitive film changes with the environmental humidity to achieve the sensor monitoring of environmental humidity changes. The sensitivity reaches 0.020 3nm/℃ when the temperature is in the range of 20℃～70℃ and -0.99nm/%RH when the humidity is in the range of 30%～80%RH. The sensor designed in this experiment can monitor a wide range of humidity variations with high humidity response sensitivity and good stability, and can simultaneously perform temperature parameter measurement, which has a large potential in the field of temperature and humidity sensing