The secondary eyewall of a tropical cyclone is located outside the primary eyewall and consists of two basic characters: a secondary convective-ring and a secondary tangential wind maximum. Based on a series of idealized numerical simulations, this paper investigates the influence of initial wind structures on the Secondary Eyewall Formation(SEF) and the key dynamic process.Resultsindicate that there is a significant correlation between the time and location of the SEF and the initial outer-core size. With decreasing initial outer-core sizes, simulated vortexes undergo canonical SEF, fake SEF and no SEF successively. The time of the SEF becomes later and the location of secondary eyewall becomes closer to the vortex center. Dynamical analysis shows that the initial outer-core size controls the distribution of Outer Rainbands(ORBs). Diabatic heating of ORBs dominates the distributions and intensities of boundary layer inflow and radial flux of absolute vorticity outside the primary eyewall. The relative intensities and positions of this radial flux of absolute vorticity and friction determine the possibility and location of the secondary tangential wind maximum. The momentum forcing can also contribute to the increase of secondary tangential wind maximum.