During software maintenance, software developers are responsible to change the software for fulfilling the change of user requirement and for fixing the design flaw. Software refactoring provides developers a behavior preserving way to enhance software structure. With proper refactoring, the refactored software would be more extendable for further change. However, during refactoring, the overall effect of refactoring on software structure is often unclear for the developer. In this work, a mechanism that provides developers to preview the refactoring effect is proposed. The refactoring effect is represented as a set of software metrics that reflect the software structure. To assess the effect of refactoring, the structure changes made by refactoring are decomposed to a series of atomic changes. The effect of refactoring on software metrics is then induced from these atomic changes. A tool: Refactoring Previewer that helps developer preview refactoring effect is implemented. The metrics change information provides by Refactoring Previewer can help developer understand the refactoring impact on software structure and make refactoring decision in more efficient way.