Abstract: Bailong buoy is the earliest deep-sea buoy to achieve operational application in the Global Tropical Moored Buoy Array in China. In order to measure accurately its basic parameters such as weight, centre-of-gravity position, initial metacentric height, and so on, two methods for designing the buoy stability test are proposed: one is a deep-sea buoy’s tilt test method, which is designed according to the characteristics of small size and quasi rotational symmetry of the deep-sea buoy and based on the conventional ship tilt test; another is a hanging test method designed according to the light weight character of the deep-sea buoy, by which the weight of the buoy can be measured directly and the three-dimensional coordinates of the buoy’s gravity center can be calculated. By means of these two methods, the weight, centre-of-gravity height, initial metacentric height, inherent period and moment of inertia of the deep-sea buoy are measured. Based on the analysis of trial error, the two methods are evaluated, showing that their trial errors are comparable, but the hanging test method is more convenient. Besides, the combination of the two methods can also be used to check the construction errors of the buoy.