The annual and interannual characteristics of convective activities over the South China Sea (SCS) in each season and the relations between interannual variations and simultaneous ENSO index are analyzed by joint empirical orthogonal function (JEOF) using the 35 a (1979-2013) monthly averaged NOAA Interpolated Outgoing Longwave Radiation (OLR), precipitation rate data of CMAP (CPC Merged Analysis of Precipitation), and ENSO index data. The results are as follows. 1) Convective activities present less change over the south of SCS between months. Over the middle and north of SCS, a persistent stage of suppressing convection is countered with another lasting active stage during a year, and the area of active convection shows abrupt bounce from south to north in mid-May and gradual retreat from north to south after September. 2) The interannual change of OLR or precipitation rate shows good consistency over the whole SCS area in autumn, winter, and spring. Convective activities in winter keep some abnormal information of those in last autumn and it lasts well until spring. 3) The interannual variations of convective activities over the SCS in autumn, winter, and spring are probably influenced by ENSO. The convective activities are restrained in El Niño status while more active in La Niña status. 4) In summer, the interannual variations of convective activities show two mainly spatial distributions, the inversion between the south and the north of SCS and the consistency over the whole SCS area. The former is probably influenced by ENSO with El Niño suppressing convection over the south and activating convection over the north; the latter has significant linear trend and climate warming makes the convection over SCS more active in summer. 5) There is abrupt change in convective activity’s abnormal status from spring to summer.