Abstract: The relation between the atmospheric heat source (AHS) over the eastern Tibetan Plateau (TP) and rainfall intraseasonal oscillation is investigated using daily NCEP/NCAR reanalysis and observed rainfall data of the middle and lower reaches of the Yangtze River during the year 1978 of drought and 1999 of flood. The propagation of low-frequency oscillation AHS over the eastern TP are studied too. The results show that the 10—20 day oscillations have important contributions to AHS over the eastern TP in summer of 1978, and 30—60 day oscillations play an important role in AHS over the eastern TP in summer of 1999. AHS over eastern TP takes on a form of intraseasonal oscillation not only in 1978 but also in 1999. And a remarkable correlation is found between AHS over the eastern TP and rainfall in the Yangtze River valley at intraseasonal oscillation period of time by cross spectrum analysis. In addition, based on 10—20 days and 30—60 days filter curves of AHS over the eastern TP in summer of 1978 and 1999, low-frequency AHS at period of 10—20 days over the eastern TP appears standing wave in zonal direction in 1978, but low-frequency AHS at period of 30—60 days over the eastern TP moves eastward to middle and lower reaches of the Yangtze River.