The meso-scale characteristics of the heavy rainfall case of 3—4th July 2003 in the Huaihe Valley is investigated based on the conventional radiosonde and surface observation as well as high resolution non-conventional observation data. It is revealed that the development of meso-β-scale convective systems within the meso-α-scale cloud belt of the Mei-Yu front results in directly the event under the favorable large-scale circulation conditions. There are three rain-mass active periods corresponding to three different peak values of rainfall intensity in the time series of the event. The rain-mass activities in the first and the third periods are related to the continuous effect of the dispersive meso-scale convective complexes, while rain-mass activity in the second period is caused by the rapid development of the near surface meso-β-scale (about 100km long) convergence line, which induces the rapid and systematic development of convective cloud cells into meso-β-scale complexes. It is also shown that these meso-β-scale convective complexes are with strong reflectivity echoes (about 40—60dBz) in the middle and low atmosphere, and there are positive correlations between the echo intensities, vertical extensions of the meso-β-scale convective complexes and the surface precipitation intensities.