This paper sums up a method for modelling development and puts forward a tool MTOOL to support the method, according to the authors researching practices in the fields of software development methodologies and tools during recent years. It induces the developing procedure and depicting means of the modelling method, introduces MTOOL s components and working procedure in detail, and gives the main grammar contents of a model specification language (MSL). The designing ideas and implementing techniques conced about MTOOL are discussed.