<p>The monitoring and application of rotational seismology have garnered increasing scholarly interest, driven by continuous advancements in measurement technologies. Rotational seismometers based on fiber optic gyroscope (FOG), with their broadband and high-sensitivity advantages, have become dominant in field measurement applications. However, observations reveal that there is a consistently significant amount of harmonic noise in the rotational records across various FOG-based seismometers, which severely interferes with the identification and analysis of valid seismic signals. Based on the characteristics of harmonic noise, we propose an adaptive harmonic peak extraction technique, which is then separately combined with Cadzow filtering and the sinusoidal interference model estimation method to suppress the harmonic noise. Experimental results demonstrate that both denoising approaches achieve effective harmonic noise attenuation while preserving the energy of background and valid seismic signals, significantly improving the signal-to-noise ratio (SNR) of the processed data. This study provides an effective solution for harmonic suppression from the perspective of signal processing, delivering higher-quality and more reliable data support for subsequent applications of rotational measurements.</p>