Abstract: In the light of the construction exper jence and welding philosophy of large oil tanks. introduced here in the paper are the mechanism of steel plate deformation. comparison and analysis of the advantages and disadvantages aTe carried out on the following six kinds of plate arranging methods. namely: "T" type. lap welding; "#" type. lap welding; "strip" type. lap.welding; "+" type, lap welding; "T" type. butt welding and"+"butt welding. which prove that different plate arranging will directly affect the bottom plate defor mation and stress extent/direction. Different stress directions cause different stress extent within the bottom plates themselves thus resulting in different extenof deformation.It is pointed out that three layer lap welding with "T" type will cause the most deformation. lap welding causes less de formation but more than butt welding. therefore multi-player with lap welding should be avoided in the arrangement ofbottom plates of oil tanks.