In order to meet the requirements of high frequency, high power, and miniaturization of RF devices, a two-dimensional model of a solidly mounted resonator (SMR) with a resonance frequency of 3.455 GHz was designed using the finite element analysis software COMSOL Multiphysics. The effects of different electrode area (200 μm2, 150 μm2, 100 μm2, 50 μm2, 25 μm2) on the lateral parasitic resonance of the resonator are investigated, and the influences of changes in the top electrode and simultaneous changes in the top and bottom electrodes on the lateral parasitic resonance of the device are compared. The lateral parasitic resonance of the device near the resonance point (3.455 GHz) increases with the reduction of the electrode area. The lateral parasitic resonance of the device is most significant when the electrode area is 25 μm2. When the amount of change in the electrode area is constant, the lateral parasitic resonance caused by simultaneously changing the areas of the top and bottom electrodes is greater than that caused by only changing the top electrode area.