Based on the 740 stations daily rainfall datasets in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the interannual variability of the intraseasonal oscillation (ISO) of summer rainfall over the Yangtze－Huaihe River basin was analysed and the associated air－sea features were discussed. The results are as follows：(1) when the ISO of summer rainfall is more active, the 30－60-day oscillation is significant in atmosphere over the Yangtze－Huaihe River basin, the Bay of Bengal, the South China Sea and the sea area southeast of Japan. In contrast, when the ISO is inactive, the 30－60-day oscillation is not significant over the above-mentioned areas. But, the ISO in the atmosphere over the equatorial Indian Ocean and the equatorial western Pacific is more significant than that in the active years.(2) In the extreme phases of ISO active years, the low-frequency Rossby wave was very significant in the low layer, centered at the South China Sea, the sea area east of Japan, and the Gulf of Alaska. Analogously, there was a significant Rossby wave in the high layer, centered at the Ural Mountains, Lake Baikal, the Sea of Okhotsk, and Sakhalin.(3) The ISO intensity showed significant positive correlation with SST in pre-spring Kuroshio and simultaneous South China Sea. The numerical experiments showed that the positive SST anomaly in pre-spring Kuroshio (simultaneous South China Sea) could excite low-frequency responds in the atmosphere which extended via the Rossby wave train and enhanced the amplitude and phase characteristics of this wave train. Moreover, the ISO intensity of summer rainfall is more active in the year after ENSO.