Previous modeling studies have found that tropical cyclones (TCs) with a larger initial overall (both inner core and outer core) size tend to have a higher steady-state intensity. Since TC size before and in steady state keeps a strong memory of its initial size, the dependence of steady-state intensity on initial size is often studied by examining the effect of steady-state size on steady-state intensity. Recent studies have ascribed the effect to an increasing contribution from the supergradient wind to intensity as size increases from the boundary layer dynamic perspective. In the present study, the effect has been revisited from the energetic perspective based on the isentropic energy diagnostic analysis using axisymmetric numerical simulations. Results show that as the overall TC size increases, the overall surface enthalpy uxes increase and thus the in ow leg in the energy cycle absorbs more entropy in larger TCs, resulting in higher generations of kinetic energy and thus higher intensities. It is also found that a higher sea surface temperature tends to reduce the effect of TC size on the entropy absorption in the TC energy cycle but results in a higher Carnot ef ciency. As a result, the increasing tendency of generation of kinetic energy or TC intensity with size is similar under different sea surface temperatures.