In the vertical， the isothermal layer and mixed layer are two parameters governing the upper ocean structure. High salinity stratification in the surface layer often limits the mixed layer depth and thus results in the interlayer called the barrier layer between the base of mixed layer and the top of the thermocline. The barrier layer acts as a "barrier" for the transfer of heat， monmentum， mass， and nutrient fluxes between the mixed layer and the thermocline， affecting the heat budget of the surface mixed layer and resultant air-sea interaction. Owing to the implementation of global ocean observation programs， scientists have gradually realized the importance of oceanic salinity in ocean circulation and climate change in the past two decades. Thus， the role of barrier layer caused by salinity in heat balance of upper ocean is the present hotspot in physical oceanography field. Focusing on the key scientific issues centered at the barrier layer variations and its climatic impacts， three aspects of it are introduced under the review：Spatial structures and multi-scale variations of barrier layer in the world ocean； roles of oceanic and atmospheric processes in barrier layer variations； key processes and mechanisms of interactions between barrier layer and weather， climate and biology. We mainly emphasize the ocean-atmosphere interactions associated with the barrier layer variations and their cliamtic impacts. Finally， we propose several issues that remian to be solved were proposed.