Abstract: The NCEP/NCAR reanalysis data and observed daily precipitation data were used to investigate the intraseasonal variability of heavy rainfall and circulation characteristics in Summer 2007. The results show that the intraseasonal variation of precipitation in summer 2007 over the Huaihe river basin was mainly controlled by the 10-25 days oscillation. The precipitation intensity in the Huaihe river basin was related to the corresponding low-frequency periods. The mostly rainfalls happened in positive phase of the low-frequency periods and ended or weakened evidently in negative phase. The precipitation low-frequency variability in the Huaihe river basin was related with the low-frequency evolvement of the western Pacific subtropical high and South Asia high and, also with the low-frequency variation of the cold airs over the midhigh latitudes. In the peak phase of the low-frequency periods, there is a low-frequency anticyclone in the higher troposphere, which caused the South Asia high to shift eastward its ridge line extending northward and favoured the westward and northward development of the western Pacific subtropical high developed, with low-frequency upward current existing in the whole troposphere. At the same time, the isentropic analysis indicates that positive potential vorticity appeared in the high-latitude areas. And the cold airs that reached southward the Huaihe river basin were more active than the normal. A favorable circulation environment for heavy rainfall over the Huaihe river basin was then formed. On the other hand, in the vale phase of the lowfrequency periods, there is a lowfrequency cyclone in the higher troposphere, caused the South Asia high to shift westward with its ridge line extending southward. The western Pacific subtropical high developed then eastward and southward with the lowfrequency sinking motion existing throughout the troposphere with the negative potential vorticity appeared in the highlatitude areas and the cold airs reached the Huaihe river basin being less active than the normal. An unfavorable circulation environment for heavy rainfall over the Huaihe river basin was formed ultimately.