Abstract: The range of tank design pressure is expanded in the GB 50341-2014 Code for Design of Vertical Cylindrical Welded steel Oil Tanks and the relevant technical requirements are also described in the code. The tank strength failure caused by the pressure was theoretically analyzed, and the effects of positive and negative design pressure on the effective cross-section area at the roof-to-shell junction, calculation thickness of shell plate, shell stiffening ring and roof structure type were illustrated. It is indicated that the calculation formula for the effective cross-section area at the roof-to-shell weak junction stipulated in the code is only suitable for Q235 metal plate. Under the working condition with small internal pressure, the cross-section area of compression ring is in conflict with the value of weak-roof structure, so they cannot be satisfied simultaneously. Under the negative pressure, the number of stiffening rings is determined on the basis of the allowable critical pressure and the maximum equivalent height of unstiffened tank shell. The research results provide the reference for tank structure design.