In this study we observed and analyzed the corrosion phenomena in leak site and the effect on temperature at the target surface of heat transfer tube material by sodium-water reaction through water leakage in liquid sodium atmosphere. Surrounding of leak hole of the specimen was damaged by the wastage phenomena due to corrosion and erosion of material, and hole size by damage of leak site was extended from 150 μm to about 200 μm. Also, the damaged size appeared in the target surface was observed to about 1000 μm diameter. The temperature of target surface increased about 70 ~ 80 ℃ by the heat of sodium-water reaction even with the small leakage of 15 ml water. From the results of EPMA and EDX analysis, damaged area are found to be covered with complex compounds such as (NaOH+Na₂O)·Fe_xO_y or (NaCrO₂+Na₂CrO₄) mixed up with the sodium oxides by sodium-water reaction and the Fe or Cr element by matrix of tube material.