Abstract: For issues of active heat dissipation performance and effective thermal conductivity of the sandwich cylinder with cellular materials, the effective thermal conductivity including the effects of active heat dissipation of the sandwich cylinder was calculated, and its relationships with the relative density and the speed of the fluid were obtained by deriving the effective thermal conductivity and thermal governing equation under the heat convection boundary conditions. By considering the effective thermal conductivity of active heat dissipation, the transient temperature of the sandwich cylinder was calculated and compared with the result obtained by finite element method. Meanwhile, the relationship between the relative density and heat dissipation performance of the unit cells was obtained, and the optimal relative density and the optimal thickness corresponding to the maximum heat dissipation index in different dividing parts were also obtained. By comparing the transient temperature obtained by theoretical solutions using the effective thermal conductivity including the effects of active heat dissipation with FE simulations, the results are nearly the same, indicating the correct effective thermal conductivity and the accuracy to calculate the temperature of the structure. At the same time, the study demonstrates that the effective thermal conductivity increases with the decrease of the velocity of the fluid and the increase of the relative density of the structure. The Square and Hexagon have the best heat dissipation capability in the same mass quantity.