In the process of power scaling large-area quantum cascade lasers (QCLs), challenges such as degradation of beam quality and emission of multilobe far-field modes are frequently encountered. These issues become particularly pronounced with an increase in ridge width, resulting in multimode problems. To tackle this, an innovative multiridge waveguide structure based on the principle of supersymmetry (SUSY) was proposed. This structure comprises a wider main waveguide in the center and two narrower auxiliary waveguides on either side. The high-order modes of the main waveguide are coupled with the modes of the auxiliary waveguides through mode-matching design, and the optical loss of the auxiliary waveguides suppresses these modes, thereby achieving fundamental mode lasing of the wider main waveguide. This paper employs the finite difference eigenmode (FDE) method to perform detailed structural modelling and simulation optimization of the 4.6 μm wavelength quantum cascade laser, successfully achieving a single transverse mode QCL with a ridge width of 10 μm. In comparison to the traditional single-mode QCL(with a ridge width at about 5 μm), the MRW structure has the potential to increase the gain area of the laser by 100%. This offers a novel design concept and methodology for enhancing the single-mode luminous power of mid-infrared quantum cascade lasers, which is of considerable significance.