The mesoscale numerical model MM5(V3) is used to simulate the heavy rain process (occurred) in North China in Autumn. Based on the model products the environment parameters such as convective available potential energy (CAPE), storm relative helicity(SRH) and (energy)-helicity index(EHI) are calculated and analyzed. The results show that the three parameters (indicate) the occurrence and development of the heavy rain. Much energy is accumulated before the heavy rain, and the rainstorm center lies in the isoline denseness which is in the south of the (low-layer) helicity center, at the same time, the severe storm take place under the condition of (big-SRH) and small-CAPE.