Tritium storage and conveyance tank is composed of 1st/2nd storage tank, three different insulating layers(polyurethane form, polyehtylene form and ceramic board), and conveyance tank. For investigating the characteristics of temperature gradient by tritium decay heat in tritium storage and transportation tank, temperature gradient experiment was carried out. From experimental result, polyurethane form layer showed the high heat resistant layer. The temperature in 1st storage tank increase to maximum 70 ℃. Max. temperature difference between 1st storage tank and polyurethane form layer was 40 ℃.