Large LNG storage tanks as liquid natural gas cryogenic pressure vessels, the cold between the tanks and concrete wall is very important. In some special cases, ultra-low temperature liquefied natural gas will enter the second vessel, then the wall will produce thermal stress, at this time the main factor to control the temperature difference between inside and outside the wall is the hot corner protection. This paper introduces the general international structure of tank insulation, and then through the theoretical derivation, gives the insulating layer, hot corner protection and formula for calculating temperature distribution of exterior wall. On this basis, gives the formula for calculating the external thermal stress and thermal protection angle is given control of the thickness of the design equation. Finally, using ADINA finite element software to establish insulation and the wall temperature field model and calculate the heat - wall structure coupled thermal stress, and through the analysis of a project example to verify the correctness of the formula. The results show that in the leakage state, temperature stress of external wall is large, indicating that it is significant to design the thickness of hot corner protection.