Abstract: Remaining useful life(RUL) prediction of the fiber-optic gyroscopes(FOG) working in the space environment is the key issue in health management of satellite. Among the literature about the reliability estimation of the FOGs based on degradation process, the current methods didn't consider the unit-to-unit variation of the equipments with the same type. Therefore, in this paper a random variable model based on Wiener process was presented to model the degradation process of the FOG for satellite. In the presented model, the drift parameter of the Wiener process was considered as a random variable to describe the unit-to-unit variation of different equipments, and the traditional Wiener process turns out to be its special case. Based on the model, the information of reliability and RUL can be obtained. The simulation results show that the proposed method can generate reasonably better results than the traditional model and thus can be potentially applied in practice.