Based on the optimized exponential-degradation model (OEDM), a novel approach for predicting the remaining useful life (RUL) of roadheader bearings under different working conditions was proposed in this study. Specifically, the exponential process was used to construct the degradation process of a single performance characteristic under variable operating conditions, the Generalized Expectation Maximization was employed to estimate model parameters, and the proposed degradation model was updated after new data was available. In the traditional exponential degradation method, the hyperparameters are only optimized, which leads to low calculation accuracy under severe working conditions. In the proposed method, the Bayesian algorithm and the Drift Brownian motion algorithm were respectively employed to optimize hyperparameters and stochastic parameters to ensure the high accuracy of the prediction results. Besides, degradation characteristics were combined with sensory data acquired through condition monitoring were used to continuously update the remaining useful life in the proposed degradation model. Finally, the effectiveness of the proposed model was verified by the simulation case and the case study. The results show that compared with the linear Degradation Model (LDM) and general exponential degradation model (GEDM), the proposed OEDM performs well in practical applications and has a higher prediction accuracy. This study provides a reference for predictive maintenance of critical parts of tunneling machinery and cost reduction of tunneling.