Quality of Service (QoS) has now become a central issue in network design and application. This article describes a distributed architecture for linking geographically distributed network performance measurement and evaluation system (NPMES) based on in-depth research on the key techniques of network QoS. The prototype implementation of NPMES and the performance evaluation criteria based on performance aggregation are carefully introduced. Our contribution is presenting a new performance evaluation criteria based on performance aggregation to access QoS. Experiment results indicate the scalable NPMES can do the real-time detection on network performance of ISPs from the end user?s perspective. The performance aggregation approach is a bran-new idea, and of a definite practicability.