Architecture transformations are frequently performed during software design and maintenance. However this activity is not well supported at a sufficiently abstract level.In this paper, the authors characterize architecture transformations using graph rewriting rules,where architectures are represented in graph notations. Architectures are usually required to satisfy certain constraints during evolution. Therefore a way is presented to construct the sufficient and necessary condition for a transformation to preserve a constraint. The condition can be verified before the application of the transformation. Validated transformations are guaranteed not to violate corresponding constraints whenever applied.