The connectivity of urban green infrastructure (UGI) can significantly improve the biodiversity and sustainable development ability of cities, which is of great significance to maintaining the health and stability of urban ecosystems. In the present study, we used circuit theory to map the landscape connectivity of UGI in the main urban area of Nanjing and identify the important patches and corridors according to current density, and then used a search window to detect barriers and to develop a landscape connectivity optimization strategy for Nanjing. 1) Habitat fragmentation in the main urban area of Nanjing was significant. The total area of the patches was about 70.45 km², and 40% of patches area had a low contribution to connectivity. The southern part of the study area exhibited the best landscape connectivity, followed by the middle and northern parts. In the south, numerous corridors clustered into net structure, and the network structure is complex. In the middle of the study area, the Qinhuai River mainly formed a circular corridor. Relatively few corridors were observed in the northern part of the study area, and the patches were isolated. 2)There were 155 barriers in the study area, and 84.5% of those barriers were >5 hm², so the landscape connectivity in the main urban area of Nanjing can still improve greatly. Although many methods have been developed and used for predicting connectivity, circuit theory has rarely been used to map connectivity in urban areas. The present study demonstrates how circuit theory can be used to map connectivity in complex landscape and to identify important habitat patches and movement corridors for conservation planning, which is an advance in mapping the landscape connectivity of UGI. The circuit theory incorporates all possible pathways and combines structural and functional corridors, which improves corridor redundancy and provides an efficient and cost-effective tool for mapping UGI landscape connectivity. The results of this study provided an important reference for Nanjing UGI networks.