As an advanced composite sandwich structure, folded core sandwich panels are expected to be applied as sound insulation structures in transportation vehicles such as aircraft and high-speed trains. However, the configuration of folded core is diverse, and previous research has mostly focused on the V-shaped folded core, while there is still relatively little research on the sound insulation performance of other configurations. Therefore, this article establishes a numerical model of a four sided simply supported M-shaped folded core sandwich panel under vertical incident sound pressure excitation, and conducts numerical simulation of its sound insulation performance based on finite element software. The theoretical predicted sound transmission loss curve of the honeycomb sandwich panel is compared with the simulation results to verify the effectiveness of the numerical method proposed in this article. Based on simulation models, the sound insulation performance of M-type folded core sandwich panel structure was systematically studied, and the qualitative influence of geometric parameters of folded core cell on sound insulation performance was discussed. Subsequently, the influence of relative misalignment and laying angle of the upper and lower layers of M-type folded core sandwich panel with double-layer core on sound insulation performance was proposed and studied, the results show that the sound insulation performance is improved when the upper and lower layers of core are staggered and stacked in the Z-shaped line step direction of the cell, and it is better than single-layer folded core sandwich panel with the same surface density; when the relative laying angle of the upper and lower layers of core changes, the maximum weighted sound insulation is achieved when the axis of the upper and lower layers of core is vertically laid, and the trend prediction curve of the mean transmission loss with the change of the laying angle of the core is obtained, providing a reference for the optimization design of sound insulation in sandwich panels with folded core sandwich structures.