Availability is a comprehensive reflection of the overall performance for a manufacturing system, so it is necessary to evaluate the impact of component changes on the availability of a manufacturing system. However, most of the existing importance measures are based on reliability change or state degradation to measure the relative importance of components, which cannot be comprehensively analyzed for multi-state manufacturing systems. The availability of a multi-state manufacturing system is influenced by time and state. Therefore, considering the synergistic effect of time and state, this paper proposes an Integrated Availability Importance Measure (IAIM) based on proportional hazards model combining with component state probability and state transition rate. This measure fully examines the time parameters, state parameters and maintenance impact of multi-state systems, and can comprehensively evaluate the relative importance of multi-state coherent system components, provide theoretical basis for further developing the availability maintenance strategy, and indicate the improvement direction for further improving the reliability of multi-state manufacturing systems. A numerical example is given to prove its feasibility, and the influence of related parameters is investigated by sensitivity analysis. Finally, a real-world case study is used to illustrate its applicability.