In order to pick up the complementary benefits of formal and informal design methods,and overcome their shortcomings to ensure the quality and reliability of software design,an approach to the combination of formal methods and informal objectoriented design methodsHOOD is proposed in this paper. The design and implementation of a mechanical supported environment for the approach is also introduced. Based on the necessary improvement on HOOD, a hierarchical objectoriented design method, the approach integrates the Z notation and other formal specification techniques.The supported environment provides the users with the convenient and flexible tools for constructing graphics,syntax-directed editors of formal notations and text,and facilities of automatic verification.