Abstract: The thermal stress of gas-phase pipe for a LNG tank is analyzed and calculated when loading and unloading materials with finite element method. Results indicate that the maximum stress is at the joint between the gas pipe and inner container, which is consistent with actual rupture location of gas-phase pipe. The results show that although loading and unloading would cause a certain amount of pressure and temperature cycling, the range of alternating stress intensity is very small, and the fatigue damage by which is ignored. The reason for structural damage is the structural stability failure due to high thermal stress. When the axial contraction of inner container is limited, the gas pipe should have sufficient flexibility, only in this way, can thermal stresses be effectively reduced to meet the stability requirements of the structure. Starting from the constraints and thermal deformation compensation, the measures to eliminate and mitigate the heat stress of gaspipe of LNG storage tank are discussed.