Most literatures studying the integration model of scheduling and maintenance decision-making for the single machine adopte the age-based maintenance policy. However, the degradation condition for the equipment is related to numerous factors such as processing object, processing environment and processing time. As a result, focusing on the systems whose state can be inspected, an integrated model of stochastic expected values is built, which takes the job sequence and threshold value for preventive maintenance as the decision variable and the minimum total expected weighted completion time of jobs as the optimization objective by adopting the combined maintenance strategy of imperfect preventive maintenance depending on conditions, minor repair and replacement after breakdown. The experimental results show that the model can more effectively avoid excessive maintenance or insufficient maintenance and reduce the holding cost for production.