Abstract: The development of large-scale oil tanks has resulted in the complexity of stress distribution and deformation situation of tank wall and tank bottom. This paper analyzes the stress of 20×10⁴ m³ extra-large floating roof tank with finite element method and assesses their spread strength by analysis and design methods. The results show that in working conditions the stress in the following locations are relatively great, that is, tank wall plates of No.3 to No.7 rings, fillet weld structure mutations, initial and final end of edge plate warping, so these locations are dangerous points of tank body. The paper proposes optimization recommendations for reducing the stress of tank wall plates and edge plates of tank bottom and improving safety coefficient to provide a reliable basis to the structure design and material selection of 20×10⁴ m³ ultralarge floating roof tank.