Optical fiber sensors for humidity and temperature measurement are extensively utilized in medical and biological applications due to their ease of integration，immunity to electromagnetic interference，and resistance to corrosion. Polyvinyl alcohol（PVA）is frequently employed as a sensing material for humidity owing to its distinctive properties. Consequently，we designed and simulated a high-sensitivity optical fiber hybrid plasmonic waveguide sensor that integrates the humidity sensitivity of PVA with the principles of surface plasmon resonance（SPR）. This sensor comprises PVA optical fibers connected at both ends to micro-nanofibers，with a metallic grating substrate positioned beneath the PVA optical fiber to enhance sensing sensitivity via surface plasmon effects. The experimental results indicate that the sensor exhibits a sensitivity of -1.749 1 nm/%RH within the 20% to 90% relative humidity range，while its temperature sensitivity is measured at -0.518 93 nm/℃ across temperatures from 20 ℃ to 90 ℃. It demonstrates a strong linear correlation between wavelength shifts and external parameters such as temperature and humidity.