Abstract：In order to reduce the economic costs, the volume of cargo tank in the giant floating liquefied natural gas facility (FLNG) has been increasing with the size of vessel, which causes severe liquid sloshing. So sloshing-induced slamming is one of the key issues in the structure design of large-scale tank, and, it is an important part to select the overall dimension of tank during design process. Dimension sensitivity of octagon tank on sloshing load is analyzed. Firstly, through finite volume numerical method, numerical experiments with a series of filling level are performed to find out the most dangerous filling level, which is 30%. Based on this, sensitivity regularity of parameters is analyzed within the design scope of tank size. The results could provide reference for main dimension design of large-scale storage tank.