A systematic software development method named “Model-oriented Transformational Software Development Method” is proposed in this paper. In this method, data abstraction is enhanced to language abstraction; the specifying of some specific software is abstracted to language specifying; the implementation of the software becomes language reducing (transformation); the process of software development here could be described as “specification+transformation”. Following these ideas, a mechanism to abstract and encapsulate languages named Garment is designed. Relationships between languages, which are classified as inheritance, shielding and extension, are described with Garment. Taking a language knowledge base as its kernel, an environment named Garden (Garment development environment) is implemented to supports system development with Garment. Finally, the system structure of Garden and some development cases are described.