A method of humidity detection based on surface plasmon resonance was proposed.Kretschmann structure was applied to excite surface plasmon polarization.Porous ceramic SiO2 was used as the humidity-sensitive material.The refractive index of porous ceramic SiO2 altered as the ambient relative humidity changed,thus leading to a shift of surface plasmon resonance angle.On this basis,the reflection spectrum was simulated and analyzed under different refractive index of humidity-sensing layer by finite element method.Furthermore,the thickness of gold film was optimized in accordance with the full width at half maximum of reflection spectrum and the formant depth.The results show that,the best thickness of gold film is 55 nm,a linear relationship between the shift of surface plasmon resonance angle and the variation of humidity-sensing layer refractive index is got,high resolution of 0.37%RΗ and high sensitivity of 0.03°/% RH are obtained.The research contributes to the realization and application of humidity sensor based on surface plasmon resonance.