Abstract: The influence of the resonance detector's electrode thickness on the sensitivity of a mass-loading Surface Acoustic Wave(SAW) sensor was studied. By using the Coupling-Of-Modes(COM) equations, the relationship between the COM parameters and the band-edge frequencies of periodic gratings was deduced. Combining the Finite Element Method(FEM) and the P -matrix model, the variation curve of SAW sensors' sensitivity with the electrode thickness was obtained. The SAW resonators with three different electrode thicknesses of 1600 Å, 1900 Å and 3100 Å were fabricated.By depositing a SiO₂ layer onto the surface center area of the resonator, the theoretical results were verified. The results show that using a SAW resonator incorporating the ST-X quartz substrate to detect the SiO₂ mass-loading, the sensor sensitivity increases at first then decreases with the increasement of electrode thickness. And the optimal normalized electrode thickness is 1.9%. The influence is the result of the propagation velocity and the coupling coefficient. By using the method of optimizing the electrode thickness, sensors' sensitivity is improved.