The online measurement of turbine wetness has great theoretical significance and practical value to the safety and economic operation of steam turbine. According to the basic theory of perturbation method, a method is proposed to realize the turbine wetness measurement by inverted microstrip patch resonator, which has a simple construction with high sensitivity. The dielectric constant changes with the steam wetness change. The resonant frequencies of different dielectric constant are simulated based on the principle of microstrip patch resonator with the wet steam as sample substrate of resonator. The effects of sample thickness, substrate thickness and dielectric permittivity on the frequency offset are discussed. The microstrip patch resonator model is designed and simulated on the HFSS and CST. The study and simulation results show that the model is suitable for the online measurement of steam wetness of steam turbine. When the steam wetness changes 1%, the resonator frequency offset is about 18 kHz, which is about 3.6 times of frequency offset of microstrip slot resonator. The model is conducive to the accurate measurement of the steam wetness.