Frequent modifications on component-based software systems are required to accommodate to the rapid changes of external requirements, and the ability of agilely adapt to changes is considered as an important metrics for these systems. Aiming at this problem, our main concern is to present an agility evaluation method for component-based systems. In this method, interior structure of a component is explored and dependencies between features (as the basic units of components) are considered as the essential causes for change propagation between components. Then, the diversities between different types of dependencies are strictly clarified and defined as change dependency degree, with change propagation graph and reachability matrix adopted to precisely measure agility. Several quantitative metrics, i.e., change scope, change closeness and change quality, are presented to evaluate agility elaborately. Finally a practical case is put forward to validate the approach.