The steel floating caisson used in modern ship building and repairing tends to be large and ultra-large. In the design of the floating caisson, this paper describes the general variation law of the transverse meta-centric height according to the working principle, structural type and up-down process and in combination with the real case analysis, finds out the abrupt variation point and the most dangerous moment of the transverse metacentric height in the up-down process of the dock wall, and proposes the optimization measures of design.