In this study, the intensity of the trough over the Bay of Bengal （BBT） and its association with the southern China precipitation, the Madden-Julian Oscillation （MJO） and the Rossby wave propagation along the African-Asian subtropical Jet stream （AASJ） are investigated on the intraseasonal time scale. The results show that the intensity of the BBT affects the southern China precipitation more directly and to a greater degree than the MJO. The peak amplitude of the BBT tended to occur in phase-3 of the MJO. The strong BBT was substantially modulated by the Rossby wave propagation along the AASJ, which was triggered by the anomalous upstream circulation similar to the pattern of the North Atlantic Oscillation （NAO）. Therefore, from the perspective of medium- and extended-range weather forecasts, the NAO- like pattern may be regarded as a precursory signal for the strong BBT and thus the southern China precipitation.