| Based on the extreme temperature index defined by ETCCDMI (Expert Team on Climate Change Detection Monitoring and Indices) from 1951 through to 2003 and monthly mean and daily data from NCEP/NCAR Reanalysis in the same time, not only the spatial and temporal variation but also then mechanics of hot summers in East China have been analyzed. The results are summarized as follows:(1)The four indexes represent different aspect of high temperature and they have different trends. Using the daily maximum temperature and minimum temperature data from 51 stations in the east of China for the period 1951-2003, the warm day index(TX90p), the warm night index(TN90p), the summer days(SU25) and the hot wave duration (WSDI) index are calculated and their inter-annual trend and temporal-spatial variation are analyzed. It seems there was a cold time in the 1960s-1970s in the east of China, after then the climate was becoming warmer. The tx90p and wsdi indexes were declining while the tn90p and su25 indexes were rising during the 1951-2003. The results of EOF analyzing shows that the spatial distribution of first eigenvector of the four indexes is similar, with the increase trend in the east of China. And the second eigenvector of the 4 indexes show an opposite variation of North and South. The changes of 4 indexes can be divided into 3 districts by using REOF.(2)Influences of the subtropical high over the Northwest Pacific on the occurrence of hot summers in East China are significant. According to the warm day index of summer, we could select 8 hot summers and 4 cool summers by one times standard deviation. Through the composite analysis, we could conclude that in contrast to cool summers the East Asian trough shallower and the subtropical high more powerful in hot summers. The hot summers occur in East China because the strong southerly winds stop the cold air South-going, and the northerly winds over the sea on the east of China obstruct tropical weather go north, thus the East China is anomalously controlled by the subtropical high.(3)Significant positive correlations have been found between the extreme high temperature in East China and SSTA of the former year form June to August, in the key region [180°E～122.5°W,12.5°S～12.5°S]. The subtropical high intensity is affected by sea surface temperature of the key region of the former year, thus affecting summer temperature of East China. This result is very important to climate predictions. (4)The criterions that two times standard deviation of warm day index have been set up, with which 1967 and 2003 have been clarified from 44 years, they called typical hot summers. In 2003, the subtropical high is more powerful than 1967. Its steady and constantly north going and west expanding are the key reason that extreme high temperature occurred in 2003. The South Asia High came up earlier and affecting scope lager than as usual in 1967. The horizontal advection of temperature plays a less important role in resulting hot summers in contrast to the diabatic factor and the vertical advection of temperature.
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