In order to understand the occurrence of the sea surface warming in the East China Sea for summer, we investigated the variability of the sea surface temperature using satellite and in-situ data and determine the difference of environmental condition causing the warming from 1998 to 2016. In this study, we considered the sea surface warming events that sea surface temperature anomaly is higher than 1oC. Sea surface warming occurred in 2004, 2006, 2013 and 2016. Especially in2016, the sea surface temperature anomaly is more than 1.5oCandthedistributionoftemperatureshowed very significant warming in the East China Sea. Compared between temperature of sea surface and air during summer, the sea surface temperaturewas significantly higher than the air temperature when sea surface warming was occurred. The sea surface warming in the East China Sea during summer was mostly caused by suppression of mixing with subsurface water since large amount of fresh water can create a pronounced salinity-induced mixed layer above the top of the thermocline. The Chagjiang Diluted Water (CDW) contributed to the upper ocean variability in the East China. The distribution of surface salinity of CDW below29 psu is similar to distribution of sea surface temperature anomaly of 1oCormore.The dominant sea surface warming events well matched with dispersion of low-salinity water, CDW.