Interactive radiation helps accelerate tropical cyclogenesis, but the mechanism is still unclear. Using idealized numerical modeling in the radiative-convective equilibrium framework, it is revealed that interactive radiation can bring forward tropical cyclogenesis by accelerating the development of the mid-level vortex. A strong horizontal longwave radiative warming anomaly in the layer between 6 and 11 km altitudes in the vortex region, caused by large concentration of ice-phased particles at high levels, is critical to the development of the mid-level vortex. This longwave radiative warming anomaly induces more upward water vapor flux (mainly in the non-convective region) and then results in more latent heating at upper levels and more sublimation cooling at lower levels. This leads to an increase of the vertical diabatic heating gradient, and then the intensification of the mid-level vortex. A stronger upward water vapor flux also produces more condensates at upper levels and further enhances the horizontal longwave radiative warming anomaly in the upper-troposphere, constituting a positive feedback and then accelerates the tropical cyclogenesis.