The heavy rain process occurred on July 15 in 2003 in Ningqiang of Shaanxi province was analyzed. Results show that the meso-α-scale convective cloud cluster resulting in this heavy rain were elliptic or round and lasted for 17 hours, and the contribution of vapor convergence at the level of 850 hPa was more important than that of southwest jet on 700 hPa to the heavy rain, and the continuous and powerful updraft supplied by the jet sub-circulation was main cause for maintaining of the meso-α-scale convective cloud cluster.