The periodic high temperature over Liaoning in the mid-summer of 2018 was related to the extreme northward meridional position of the subtropical high. Using NCEP/NCAR reanalysis data from 1981 to 2018, ECMWF reanalysis data, and China surface climate data daily data set (V3.0) , based on the pentad time sca1e, the formation and causes of atmospheric circulation anomalies are analyzed to explain the causes and influencing mechanism of the extreme northerly subtropical high in the mid-summer of 2018. As shown by results, there are three main factors affecting the northerly position of the subtropical high. First, the ridge of high pressure over Europe developed and moved eastward, and combined with a broken branch of the subtropical high, making the subtropical high move northward. Second, the activity of cold air in the southern hemisphere leads to the strengthening of the northward cross-equatorial flow, which leads to the northward shift of the intertropical convergence zone (ITCZ) and further the northward shift of the subtropical high. Third, due to the increased sensible heat over the eastern part of the Tibetan Plateau, the updraft subsided over Liaoning and Bohai Sea in one to two pentads. The combined influence of the three factors resulted in the extreme northerly position of the subtropical high.