Abstract: In this paper, a QoS scheme is given to support applications with QoS requirements under resource constraint in open system. Specifically, a series of abstract structure, describing characteristics of end-to-end applications and system resources, as well as algorithms supporting the realization of QoS, are designed in this paper. The scheme addresses common problems found in open systems supporting QoS guarantees, such as lack of harmony QoS expressiveness, ect. In order to let as many as possible applications get system service at the same time, the scheme also supports QoS dynamic degradation.