Abstract: The impact of monsoon gyre on tropical cyclogenesis is studied based on a series of idealized numerical experiments using the non-hydrostatic Advanced Weather Research and Forecasting model (WRF version 3.3.1). Numerical results show that the large environmental vorticity of monsoon gyre is not conducive to the rapid development of tropical cyclones. Although the monsoon gyre has large initial vorticity, the radial gradient of its vertical vorticity is relatively small due to its large initial size. The radial vorticity gradient can modulate the merging of convective cells through the "vorticity segregation" effect in the initial phase. As the disturbances organize, the inflow advection of vorticity becomes increasingly important. The position of convective cells relative to the radius of the maximum wind can influence the tropical cyclone genesis. Meanwhile, there is a significant positive correlation between the environmental vorticity and tropical cyclone size. The vortex, which has a large initial size, can develop into a large tropical cyclone at the mature stage. From the thermo-dynamical point of view, a relatively large environmental relative humidity is favorable for tropical cyclogenesis since the large environmental relative humidity can induce sufficient convections inside and outside the radius of the maximum wind. The former can provide abundant diabatic heating, which further lowers pressure in the tropical cyclone center and thus is conducive to the rapid development of the tropical cyclone.