Supported by RS and GIS technology, combining the achievements in previous researches and numerous field investigations, we used Landsat-TM images of 1984, 1989, 1992, 1996, 1998, 2004 and Landsat-ETM image of 2002 as an information source to investigate thoroughly and monitor dynamically the wetland resource of Beijing, including wetland type, area, distribution, wetland exploitation, etc. The images of 1996 and 2002 were taken in May, and the remaining in September or October after flood season. We processed images selected using PCI 9.0, and then translated the format into Geotiff format. We set up interpretable symbols of different types of wetland, including reservoir wetland, river wetland, lake wetland, division canal, rice paddy and fishpond. Then images vectorizaton was carried out for spatial analysis and data statistics using ArcGIS 9.0. On this basis, taking the five-river system as an example, we can analyze the dynamic changing trend and evaluate water quality covering 1991 to 2000 using Nemerow Index. It turned out that: the areas of wetland in 1996 and 1998 were larger than those of the other years, reaching 677.29 km2 and 505.84 km2 respectively, and after 1998, the wetland resource degenerated sharply, especially rice paddy wetland. From 1998 to 2004, the area of wetland dropped 46.0%. Furthermore, the water quality of five-river system has a declining tendency, mainly due to precipitation decrease and human destruction. Finally, some countermeasures are put forward on how to use and protect the wetland eco-environment of Beijing.