Abstract: There are two main technol-economical indices for the design of inner floating roof tank: value A, the steel consumption(volume) per cubic meter in the construction stage; value B, the effective coefficient after the tank is put into service. If value A is small and value B is big, lower construction cost of the tank and higher effective utilization coefficient of the tank, as well as the economical benefits will be achieved within its service life. But, value B will be affected with many factors, including relationship between the inside diameter and the shell hight of the inner floating roof tank, the size of annular breather and its location size, alarming mode in controlling the high level and the level height, the column height of the outside ring-belt above the upper surface of the inner floating deck and the curvity radius and so on. It is believed that design is economical and reasonable when value B is more than 0. 9.2, and that the operation capacity of tank may be influenced by the type and height of the outlet. It is suggested to install the annular breather on the roof, use metal hose as inlet and outlet pipe, not use the spiral staircase without triangular rack, and not necessarily weld its columns onto the tank wall so as to improve value B. Based on the circumstances of design and construction of tank in China, it is considered that the concerned design standards of tank to be drawn up should be as soon as possible in accordance with international standards, the national standard for closed tank should be set forth with current international method.