Abstract: This paper introduces tank wall thickness calculation formulas in tank technical codes (GB 50341, JIS B 8501, BS EN 14015 and API 650), and comparatively analyzes the differences of the 4 codes in tank wall thicknesscalculation formulas, the allowable stress of tank wall steel sheet and tank wall welded joint efficiency. The comparisonresults show that besides the differences in allowable stress and welded joint coefficient, design liquid level height oftank wall calculation thickness is also different, and the main factor causing tank wall thickness variations is the different understandings for design liquid level height, and moreover, the tank wall thickness calculated using the relevant calculationformulas given in GB 50341 and other tank codes is consistent. In order to make the calculated tank wall thickness in linewith the international standards and codes, allowable stress determination principles are given, and design liquid level heightis re-defined in this paper. It is proved through field cases that the determination principles are reasonable and reliable.