Abstract: The effect of urbanization on the stream structure and connectivity has been a hot topic nowadays. At present， fast urbanization has caused many environmental problems， such as the simplification of water system structure, decreasing connectivity of river and degrading water quality. Three remote sensing images in 1990,2000 and 2010 in the center of Nanchang were processed and classified for the analyses on the spatial and temporal characteristics of underlying lands．The river systems were extracted by GIS based on the topographic maps in 1958 and 2010， and the influence on the stream structure was analyzed using quantitative and structural index; The graph method was used to analyze the changes in river connection. The results showed that: (1) During the 20 years, the urban land area increased by 17473 km2, and the water area decreased by 3404 km2. The water area decreased with the increase of urban land; (2) The water surface rate, river network density and frequency were found to decrease. Tributary development was also found to decrease during the urbanization process; (3)The connectivity of water system reduced at the north of the Ganjiang River but increased at the south. Key words：water system pattern;connectivity;urbanization;index system;Nanchang City