Abstract: In the postulated nuclear core melt accident, a stratified molten pool configuration would be formed in the lower head of the nuclear reactor pressure vessel. The formation of the heavy metallic layer leads to the decrease of the height of the thin metallic layer, consequently, the thermal focusing effect in the sidewall of the top metallic layer would be enhanced and it is possible for the vessel failure. The heat transfer behavior of thin metallic layer experiment for the low aspect ratio (HELM LR) was performed to investigate the heat transfer in the thin metallic layer under the low aspect ratio condition. The experimental results indicate that Churchill-Chu correlation is still suitable for lateral heat transfer calculation under the low aspect ratio condition. Its calculated results are slightly less conservative under the condition of the low aspect ratio and water as the simulant. Applicating the Churchill-Chu correlation to the molten pool in the nuclear reactor case, it is found that increasing the decay power of the oxidic layer and decreasing the height of the thin metallic layer might lead to the failure of the hypothesis of isothermal boundary for the oxidic layer. The thermal focusing effect of the sidewall still increases with the decrease of the height of the thin metallic layer, but the increasing rate becomes slow.