Abstract: An extension approach to the design of distributed real\|time systems is presented. Based on the transformational design approach, this method supports the extension or change of the system specification. The trace part of the new requirement is described by trace logic, and the time part is described by DCI(Duration calculus implementable). A set of standard extension rules help generate the new design specification from the old one. A case of the multi user multi media system demonstrates our method in detail.