With the increase of cargo load，the enlargement of ships and the requirement of high permeability in the sea area，slender high square caissons are becoming more and more common，but the floating stability of slenderer caissons is poorer. To study the floating stability of slender high square caissons，the length，width and height of regular and symmetrical caissons are transformed into 5 groups respectively，and the characteristics of floating stability parameters of square caissons with different shapes and sizes are summarized. The conclusions are that：1）The smaller the plane size of the slender rectangular caisson，the greater the relative draft required to meet the floating stability，and the worse the floating stability.2）The total width of the caisson is the most important parameter affecting the floating stability. The effect of the total length on the relative draft is far less than that of the total width. 3）When the caisson height is small，it has a greater impact on the relative draft. However，with the increase of the caisson height，the relative draft will tend to be constant.