Patterns of river systems and hydrological connectivity in different river basins are changing significantly, mainly due to the effects of climate change and human activities. This may lead to a series of water resource problems such as floods and droughts. In this paper, we took the whole Lake Poyang Basin as our study area, and used graph theory to construct the evaluation systems based on the extracted river data of five periods during 1989-2020 by using Google Earth Engine (GEE). Therefore, we aimed to quantitatively analyse the spatial and temporal evolution of the river system pattern and structural connectivity in the study area. According to the data of catchment topography, land use and normalised difference vegetation index (NDVI), we used the index of connectivity (IC) to evaluate the spatial and temporal changes of functional connectivity, and further discussed the relationships between hydrological connectivity and runoff-sediment discharge. The results showed that the rivers in the Lake Poyang Basin had changed significantly over the past 30 years and tended to be more complicated. The number and length of rivers showed an increasing trend (except for the main rivers of the basin), and the associated changes occured mainly in the northern regions of the basin, especially for third class rivers. The water surface ratio, river development coefficient, drainage density and complexity showed a clear increasing trend. Moreover, the rate of change after 2000 was about twice as high as before. In general, river network connectivity, node connectivity and river network connectivity in the catchment showed increasing trends, and structural connectivity was in good condition with little variation. Functional connectivity analysis showed that IC values were generally high in flat areas close to the main downstream river channel, while IC values were relatively low in densely vegetated areas far from upstream river channels. Over the last 30 years, IC had shown decreasing variation and marked spatial heterogeneity. Statistical results showed that IC had a significant positive correlation with annual runoff and sediment discharge (correlation coefficient is 0.6 and 0.7, respectively). In short, the river structure in the Lake Poyang Basin had changed significantly, and the structural connectivity showed an increasing trend, while the functional connectivity of the discharge and sediment transport process gradually decreased after 2000. From the perspective of basin structure and functional connectivity, the results of this paper can provide scientific reference and support for relevant studies on the development of river system connectivity and water-soil resource management in the Lake Poyang Basin.