In the 21st century, global warming hiatus has become a new hotspot in the research of climate change. This paper introduces the research progress on this phenomenon in detail, especially the validation studies of hiatus, research on the influence of the radiation forcing and the natural variability of the climate system due to airsea interaction, and then puts forward several puzzles that still need to be solved on current research of hiatus. The paper particularly introduces the international major view, which think that the main reason of the hiatus in this century is that the strengthened trade wind on the background of the PDO negative phase leads to the warm water "accumulation" in the equatorial western Pacific while the cooling in equatorial eastern Pacific causes the heat transferred down to the deep ocean. Therefore, hiatus phenomenon does not mean the stop of global warming, but just the heat transportation to the deep ocean, which is another manifestation of global warming.