Abstract: The analyses on deformation inspection data and stress inspection data of tank bottom plate are made, including the problems existed in inspection program of bottom maintenance. It is pointed out that the major reason of deformation of tank bottom plate is from two facets, the first is the hoop convergent force of tank shell welds and fillet welds of bottom plate, and the second is the spreading pattern between edge plate and bottom plate. The authors consider that rational welding sequence and multi-plate skip welding method can effectively suppress the wave-type deformation of bottom welding.