Model refactoring is emerging as a desirable means to improve design model by restructuring it while preserving the behavior properties. It applies the concept of refactoring to a higher level of abstraction and makes refactoring more convenient and effective. Model refactoring always arises at design phase, but unfortunately, 7(days) times 24(hours) high availability requires that refactoring takes effect at runtime without stopping the running systems. In this paper, we present a middleware-based approach to applying model refactoring for component based applications at runtime. First of all, ill-structures in an application are abstracted as bad patterns, each of which has at least one good pattern abstracting the refactored part in the application without the ill-structure. People can define the bad/good patterns using a MOF-based metamodel. After that, with the help of middleware, the ill-structures will be automatically detected and removed by refactoring the running application under the guide of predefined patterns.