Abstract: The five-hundred-meter aperture spherical radio telescope (FAST) is the largest radio telescope in the world, which is located in the natural karst terrain of Guizhou province. The low noise receiver system of FAST requires high performance orthomode transducer (OMT), so, this paper proposes a quick and efficient design method of broadband quadruple-ridge waveguide orthomode transducer (OMT). First, two critical parts of the OMT are designed separately, and then the overall optimization is carried out. In order to improve in-band impedance performance, stepped impedance matching rings are introduced into two orthogonal probes. An L-band quadruple-ridge waveguide OMT developed by this method is designed for FAST with reflection coefficient smaller than -20 dB for both polarizations, polarization coupling level lower than -43dB, and the insertion loss lower than 0. 15 dB over the entire operational bandwidth. The experimental results are in good agreement with the simulations. The design method proposed in this paper is suitable for the design of broadband quadruple-ridge waveguide OMT in various frequency ranges.