A persistent extreme high temperature(HT) event occurred in southern China in late spring of 2018.It began on May 15 and developed rapidly in the Jianghuai region,then spread southward to southern China beginning May 17,and remained in the region until early June.The HT days in the southern reaches of the Yangtze River and east part of southern China are approximately 6-10 days greater than the climatology.The accumulated HT frequencies with maximal air temperatures over 35℃ reach nearly 2 000,which is 2.6 times greater than the second largest value in the research period.In May 2018,more than 1/3 of the stations in southern China broke the historical records of HT days of May.The statistical analyses show that the HT days in southern China in late spring (May 16-31) are significantly related to the 500 hPa geopotential heights and convection over the area,as well as the 850 hPa meridional wind speed over its west side.However,the effect of the convection is more advanced,with a leading influence of about one week.Aside from the local circulations,the convection over the tropical Indian Ocean has a significant negative correlation with the HT frequency.A case study of circulations in 2018 also supported this statistical result.The spatial differences of convection may be linked to the activities of MJO.In May 2018,MJO remained in phases 1 and 2 for 20 days with amplitudes exceeding 1.The days in these two phases are the largest in May since 1981.Both the statistical analysis and case study indicate that MJO has an important impact on the HT events in southern China in late spring of 2018.