Optomechanical systems based on the silicon nitride (SiN) membrane and Fabry-Perot cavity have important application value in quantum physics and precision measurement. The tunability of the resonant frequencies of the SiN membrane is significant for controlling the interaction between the light field and the membrane. In this paper, a method based on high-frequency nonharmonic excitation to adjust the resonant frequencies of the SiN membrane is proposed and demonstrated experimentally. First, we establish the theoretical frequency-response model of the SiN membrane resonator with a high-frequency nonharmonic excitation. Then, a fiber-optic Fabry-Perot interferometer is constructed to measure the vibration of the SiN membrane. Experimental results show the resonant frequencies of the SiN membrane can be adjusted by controlling the exciting voltage. The frequency shift of fundamental mode is more than that of high-order modes. Further, the proposed method is used to stabilize the resonant frequency of the SiN membrane, and the corresponding frequency shift rate is 1/200 of that without excitation. This paper provides a simple and robust method for stabilizing the resonant frequencies of SiN membranes and for controlling the linear and nonlinear coupling between mechanical modes and multi-mode cavity optical force interaction.