In order to solve the problem that existing degradation models for nonlinear electromechanical systems under intermittent faults fail to simultaneously consider the effects of imperfect maintenance and degradation coupling, which leads to a decline in prediction accuracy, a remaining useful life prediction method based on intermittently composite degradation model is proposed for nonlinear electromechanical system with intermittent faults. Firstly, the bond graph model of the nonlinear electromechanical system is established for fault detection and isolation, and an augmented water flow optimizer algorithm is developed for intermittent fault estimation. Secondly, a hybrid intermittent fault feature is extracted based on the tumbling window to comprehensively describe the intermittent fault trend. The intermittently composite degradation model is proposed to predict the remaining useful life of faulty component in the situation where the imperfect maintenance and degradation coupling effect exist simultaneously. The model divides the degradation process of the faulty components into internal and external degradation, and describes the effects of degradation coupling and imperfect maintenance through coupling factors and a geometric reduction of intensity model. Experimental results show that the proposed method achieves cumulative relative accuracy of 97.53% and 96.80% in predicting the remaining useful life of multiple intermittent faults, which is superior to the particle swarm optimization algorithm and the water flow optimization algorithm. Additionally, in comparison with degradation models considering only degradation coupling effects and only imperfect maintenance effects, the proposed method demonstrates significant improvement in prediction accuracy.