In 2006, Taiwan joins the Asia Pacific Economic Cooperation (APEC) regional GNSS test bed demonstration project, the goal is to facilitate the implementation and operation of a satellite based aviation navigation system. The reference stations are placed in seven economies including Indonesia, Malaysia, the Philippines, Thailand, Vietnam, Australia and Taiwan. Among them, Australia uses one reference station from its current GRAS network and the reference station in Taiwan is developed by National Cheng Kung University. This APEC regional GNSS test bed is operational in September 2006. For the further extension of this network in Taiwan, we develop a GNSS augmentation system evaluation module which includes several reference station modules and one master station all with low-cost and flexible architecture, and we could quickly implement this GNSS augmentation system evaluation module in a region with interested. This paper presents the architecture of this GNSS augmentation system evaluation module. This evaluation module includes several GNSS reference station modules and one master station module. The reference station software could process the GNSS observation data from the GNSS receiver into a designate message formats, and then transmit these messages to the master station module via Internet. Because the communication link is Internet, the master station software needs to synchronize incoming messages from the time delay caused by Internet, then the master station decode all of the messages for monitoring, differential corrections processing and observation data logging. All these processes need to be done in real-time. The main hardware components in a reference station module include a dual frequency GNSS receiver, a portable computation processor, and the communication ports. For the reference station module we use a module computer with Microsoft Windows XP operating system as the platform, and this system can be reproduced quickly and easily with a flexible architecture. For the master station we use a similar architecture with a higher performance CPU and a larger data storage drive. After the development of this GNSS augmentation system evaluation module is completed, we will place this module at some airports in Taiwan to evaluate the enhancement of the GNSS services provided by this module. We will compare this GNSS regional evaluation module with the APEC GNSS test bed, and we will also show the GNSS performance comparison between this module and the MSAS in Taiwan.