Abstract: The Key problem of developing multimedia courseware authoring system is how to present the instruction flow and presentation.GNT(Generalized Transition Network) is used to describe instruction flow and instruction content is expressed by PC(Presentation Context)in multimedia courseware.In the meantime,how to use them in BUAA-MCAS(BUAA Multimedia Courseware Authoring System) is discussed. It includes how to describe instruction flow with GTN and how to present instruction contents with presentation context.The internal data structure is also given.These methods in BUAA-MCAS have two characteristics.First,the description of instruction flow and presentation of instruction contents are separated,which makes the courseware authoring system flexible.Secondly,instruction contents can be concurrently presented by expressing the instruction presentation with presentation contexts.