A data buoy, when moored at the sea, will be influenced by different environmental factors such as wind, wave current etc.For this reason, the stability of data buoy is of great importance. This paper describes the analysis and calculation of the stability of a data buoy which has a weight suspended from its bottom under normal working conditions and the influence of the distance from the weight to the bottom of the buoy on the “righting” ability of the buoy when it is capsized. The paper also provides the curves which show the influence of the size of the weight and the distance from the weight to the bottom of the buoy on the “righting” ability of the buoy. All these are of great reference value for the design and use of data buoy at sea and also for the design of similar floating bodies. The results from calculation agree quite well with those from the model experiment. A data buoy, when moored at the sea, will be influenced by different environmental factors such as wind, wave current etc. for reason, the stability of data buoy is of great importance. This paper describes the analysis and calculation of the stability of a data buoy which has a weight suspended from its bottom under normal working conditions and the influence of the distance from the weight to the bottom of the buoy on the “righting” ability of the buoy when it is capsized. The paper also provides the curves which show the influence of the size of the weight and the distance from the weight to the bottom of the buoy on the “righting” ability of the buoy. All these are great reference value for the design and use of data buoy at sea and also for the design of similar floating bodies. The results from calculation agree quite well with those from the model experiment.