It is difficult to obtain failure data in stability analysis of long lifetime gyro such as hemispherical resonator gyro. Therefore, traditional stability analysis methods based on failure data is useless in stability analysis of long lifetime gyro. A stability analysis method based on probability statistics is proposed in this paper to solve this problem. In this method, Weibull distribution is applied into cloud model, which is an uncertain transformation model based on fuzzy mathematics and probability statistics. Weibull cloud model takes fuzziness, randomness, and the connection between them into consideration, and it can analysis the stability of hemispherical resonator gyro without failure data based on probability statistics. In this paper, the inference rules of Weibull cloud model and construction method of cloud generator are given, and the estimation method of parameters is derived from normal cloud model. A series of output data of hemispherical resonator gyro is used to establish Weibull cloud model and analysis the longtime stability of hemispherical resonator gyro, and the results show that this method can analysis the stability of hemispherical resonator gyro effectively without failure data.