The stability of platform is important to ensure the platforms are safe, especially during the mooring line breaking process in typhoon condition. The paper presents a stability analysis method for floating platforms of the mooring line breaking process based on the time-domain analysis. The time-domain simulation during the mooring line breaking is provided. The time of the mooring line break, the max tilt angle of platform and the amended equivalent overturning moment are calculated for the stability analysis. The results show that the platform would have a serious tilt when the mooring line breaks, this increases the overturning moments and may cause the platform not meets the stability requirements during this process. It is necessary to pay attention to the stability problem during the mooring line breaking process in typhoon condition. And properly locating the down-flooding points is recommended to avoide the stability problem.