This paper explores the effect of nonlinear disturbance of a static pressure oil pad in an optical astronomical telescope on the tracking accuracy. Firstly, the causes of oil pad disturbance are analyzed and the frequencies of nonlinear disturbances are measured accurately with accelerometers and an encoder. By analysis of the vibration curve of the accelerometer, the position curve and Fast Fourier Transfer(FFT) curve of the encoder when the oil pad is turning on or turning off, it points out that the vibration of oil pad is narrow band interference. Then, a Notch filter is proposed to suppress the oil pad disturbance by setting the central frequency at the main disturbance frequency. The design process of the proposed method is discussed in detail. The bode diagram and the zero-pole map of Notch filter are given. When oil film thickness needs to be changed, the Notch frequency band can be adjusted flexibly by changing the parameters of Notch filter. Finally, the control system with Notch filter is implemented and filtering results are shown. Simulation and experimental results of tracking and pointing on a 2.5 m astronomical optical telescope indicate that the tracking precision of the azimuth system is 0.083 7″RMS and 0.571″PV by measuring and eliminating the main noise at 0.825 Hz .As comparing with pressure fluctuation attenuation devices, the proposed method shows the advantages of convenience, flexibility and good universality.