Honeycomb sandwich panels are widely used in aerospace and other major equipment because of their light weight and excellent mechanical properties. The acoustic performance， however， is a significant flaw. In this study， a sound insulation predic? tion model of infinite honeycomb sandwich panel is established based on the Bloch theorem and the wavenumber finite element method. The honeycomb sandwich panel is simulated with a periodic cell. By analysing the dispersion characteristics of the honey? comb sandwich panel in the wavenumber domain， the sound insulation mechanism under the excitation of diffuse sound field is re? vealed， and the influence of geometrical parameters on the sound insulation performance of the honeycomb sandwich panel is inves? tigated. The results demonstrate that below the critical frequency， the sound insulation of the honeycomb sandwich panel is mainly controlled by the mass law， while above the critical frequency， the sound insulation is also impacted by the structure's own feature wave. When the incident acoustic wave excites the resonance of the feature wave， the sound insulation fluctuates with frequency and generates a sound insulation valley. The effect of thickness variation on the sound insulation performance is primarily related to the amount of sound insulation below the critical frequency， the thicker the honeycomb sandwich panel， the higher the amount of sound insulation； height increase reduces the mass law control zone and shifts the first sound insulation valley to lower frequencies， resulting in a weakening of the overall sound insulation performance. The relevant research results can provide a reference basis for the design of vibration and noise reduction of complex structures.