The paper presents a joint predictive maintenance and spare parts provisioning policy for gradually deteriorating multi-component systems with complex structure. The decision-making process related to maintenance, spare parts ordering, as well as inspections scheduling is based on both RUL prediction and structural importance measure. Moreover, economic dependency between components is studied and integrated in decision rules. In addition, the impacts of the system structure on components deterioration process are also investigated. This dependency may have a significant influence on the RUL estimation of components. In order to evaluate the performance of the proposed joint predictive policy, a cost model is used. Finally, a numerical example of a 6-component system is introduced to illustrate the use and the advantages of the proposed joint maintenance and spare parts provisioning policy.