The conventional circuit breaker is one kind of complex mechanical system. The remaining useful life (RUL) prediction of its operating accessories is essential for maintaining the reliability of the circuit breaker. To accurately grasp this RUL, this article proposes a remaining mechanical life prediction method of operating accessories for the conventional circuit breaker based on Wiener process. First, the action time of operating accessories is selected as the performance degradation feature by analyzing the coil current waveform during the operation process of the operating accessories. The performance degradation process of operating accessories is linear and nonmonotonic. Hence, the performance degradation model is established by employing Wiener process. The maximum likelihood estimation method is utilized to estimate the parameters of the degradation model. Then, based on the concept of first hitting time, RUL prediction model is formulated and its probability density function is derived, which realizes the RUL prediction of operating accessories. Finally, the whole life tests and the RUL prediction for the shunt release and the release electromagnet as operating accessories installed in the conventional circuit breaker are carried out. The prediction results demonstrate the effectiveness of the proposed method.