In the existing methods, only the maintenance decision of a single device is taken into consideration, the maintenance strategy of the system and the joint inventory optimization of spare parts are neglected. The paper proposes a system's maintenance and inventory joint decision model based on remaining useful life prediction under imperfect maintenance. Firstly, based on the Wiener process, the degradation of the equipment affected by imperfect maintenance is modeled, and then the remaining useful life probability distribution of the equipment is derived. Secondly, the detection interval, the preventive maintenance threshold, the maintenance times threshold and the inventory are used as decision variables to establish a cost-time ratio joint decision model, which realizes the optimization of system's maintenance decision cost. Finally, numerical simulation experiments show that the maintenance cost of the proposed method is reduced by 1. 5%, compared with that of the method based on a single decision variable.