Abstract: The floating state of the bottomed-hollow cylinder is analyzed as compared with a solid cylinder with the consideration of the water intake at the top. The cylinder may stably float in the vertical posture when it is filled with the water or is in an inverted position in the water. As the water volume inside the cylinder is reduced, the balance position will be tilt after a fork bifurcation, and topple over finally. Calculation results of the relevant formulas and the photographs of various floating states are given for glass cups.