The permanent Arctic halocline, one of the particular structures in the upper Arctic ocean, is very important to the maintenance ofthe sea ice and cold surface layer in the Arctic ocean. In the last decade, a large-scale change occurred in the Arctic climatic system, which had never been observed before 1990s. At the same time, the Cold Halocline Layer (CHL) of the Arctic ocean experienced a special evolution with disappearing at the early 1990s and then partially recovering in 1998. In this circumstance, the Arctic halocline became a new focus of the Arctic ocean research. The recent advances in the studies on the Arctic halocline, including the mechanism for its formation and observations of its inter-annual variations, were reviewed in this paper. The unsolved problems in the previous research works and possible advances in the future studies were also commented.
    Several theories of the formation for the Arctic halocline had been presented, such as “Advective CHL” and “Convective CHL”. Because the surface salinity in the Eurasia basin had increased, the CHL in the Eurasia basin should be “Convective CHL”. The “Advective CHL” mechanism might be suitable for the halocline in the Canada basin as its characteristics is quite different from that of the CHL in the Eurasia basin. Since 1990s, a series of anomalous variations had been found,such as the retreating of CHL, the warming of the Atlantic layer and the decreasing of the Arctic sea ice. In fact, all these variations are connected closely.The partial recovery of the Arctic halocline implied that the observed variations in the Arctic climatic system could be a kind of periodical oscillation.