Abstract: The connectivity of marsh wetlands is crucial for birds that rely on these habitats for survival. The Nenjiang River Basin contains numerous marsh wetlands, serving as important habitats and stopover sites for migratory birds. This study utilized a long-term annual dataset of surface water and applied a curve-fitting method to identify abrupt change points in order to determine the threshold distance for marsh wetland patch connectivity. The Integral Index of Connectivity (IIC) was selected to quantitatively assess the spatiotemporal changes in marsh wetland connectivity within the Nenjiang River Basin from 1984 to 2020. The importance index (dIIC) of different wetland patches was calculated to identify key patches critical for maintaining marsh wetland connectivity. Furthermore, and the influencing factors affecting marsh wetland connectivity were analyzed. Research results indicate that the threshold distance for marsh wetland patch connectivity in the Nenjiang River Basin is 8 km. The connectivity has shown a decreasing trend over time, with the period from 2001 to 2010 being a critical phase that contributed significantly to the overall decline in connectivity between 1984 and 2020. Spatially, marsh wetlands are predominantly distributed in the downstream areas of the Nenjiang River Basin. The marsh wetlands located at the confluences of tributaries and the main stem of the Nenjiang River, as well as the river floodplains along the main channel, are identified as key patches influencing basin-scale connectivity. Single-factor statistical analysis revealed a strong correlation between annual precipitation and IIC, primarily due to its positive indirect effect on marsh wetland area. Multi-factor statistical analysis indicated that marsh wetland area is the most significant factor influencing IIC, exhibiting a direct positive response effect, followed by the number of water conservancy projects, which exert a negative response effect. This study provides a scientific reference for the conservation of bird habitats and wetland management in the Nenjiang River Basin.