The classical component importance analysis considers the reliability only with little attention paid to economic factors. This paper proposes a new model and new measure of component importance for all-digital protection systems， which considers both the manufacturing cost and the failure cost. First， the function of the manufacturing cost versus the component failure rate is proposed， and the function of the total cost versus system reliability for all-digital protection systems is further derived. Second， the importance measure considering cost with respect to the component as well as component type is defined， and the related calculation equations are derived. Finally， the component importance for a typical all-digital protection system is analyzed and discussed. The results show that the new measure is more dynamic and responsive in the sense of being able to provide importance ranking for the importance of the components included in the all-digital protection systems. As a result， the new measure will be more informative and helpful to designers in optimizing system reliability.