Abstract: Broadband Fabry Perot (FP) cavities have been widely used in high-precision astronomical spectral calibration in recent years. Achieving calibration accuracy better than 1 m/s requires the stability of the FP cavity to be better than 10⁻⁹ (<MHz). However, coating aging, phase transition of spacer materials, and long-term environmental changes can cause a slow drift of the FP cavity, affecting the long-term repeatability and accuracy of wavelength calibration. To track the drift of the FP cavity and improve its long-term calibration accuracy, a high-precision laser scanning tracking system was designed using a rubidium absorption cell as the absolute frequency reference. Theoretically, the frequency accuracy can reach 10⁻⁹ or even higher near the rubidium absorption line. However, the FP etalon FSR (Free Spectral Range) used for wavelength calibration is usually 15 to 60 GHz, which means the peaks are likely far away from the rubidium lines. Therefore, accurately calibrating the scanning frequency of the laser is the key to expanding the measurement range and maintaining measurement accuracy. We use a small FSR auxiliary FP cavity with rubidium absorption cells for precisely calibrating laser scanning frequency. To select the parameters of the system's key components, the laser scanning frequency calibration of two materials, and different FSR auxiliary FP cavities under different detection conditions (temperature changes, noise levels) are simulated. The simulated results show that the auxiliary FP cavity with FSR below 70 MHz can achieve calibration of MHz frequency accuracy without considering environmental and detection factors; meanwhile, the smaller the FSR, the more sensitive it is to temperature changes and detection noise. Taking into account the simulated results and fabrication difficulty, the optimal FSR for the auxiliary FP cavity is 30−70 MHz. Since the temperature drift coefficient of the anti-resonant hollow core fiber FP cavity is much smaller than that of the traditional fiber FP cavity, it is also more suitable for high-precision frequency calibration.