Hydrologic connectivity (HC) is a key index for reflecting the process, storage-discharge capacity, and effectiveness of aquatic ecosystem restoration on a watershed scale. Meanwhile, it is also an important way to resolve water problems in a nation. Therefore, it is necessary to summarize the research progress in HC. Based on a summary of available research, the concept, type, evaluation method, theory system, and application of HC was summarized. The narrow concept of HC refers the degree to which water-mediated transfer of matter within or across a spatially heterogeneous landscape or patches, while the narrow concept of HC means the degree of connection to all kinds of eco-hydrological and biogeochemical processes across spatio-temporal scales within or between the earths outer spheres. The current HC evaluation methods were generalized as in-situ monitoring, hydrologic model, connectivity functions, and graph theory. All of these methods were concentrated in a quantitative expression of the surface hydrological structure connectivity within watersheds, which cannot be applied on other scales. The study of HC theory is still lagging behind practice and is not systematic. Finally, applying HC to influence the storage capacity of freshwater in plains areas and restore the riverine system was introduced briefly. In the future, HC evaluation methods could quantify integrated HC across space and time combined with geological information technology and the feld monitoring data. For the application of HC, the directions of future study were discussed, including the principles around connectivity engineering, storage characteristics, and the best storage-discharge regulations for different stream structures. The integrated model framework should contain all kinds of key modules, e.g., the impacts of climate change and anthropogenic activities, ecological processes, and restoration cost and value, and which can identify the critical factors for indicating restoration processes or effects. These fndings may provide a theoretical basis for managers to restore ecosystems or adopt adaptive countermeasures.