In this paper, the ASRH (Average Storm-Relative Helicity) is introduced and the expression of ASRH is given to analysis of a heavy rainfall event according the theory of storm-relative helicity.In the diagnosis of storm-relative helicity，we considered the effect of upper and lower level storm-relative helicity at the same time.A diagnosis is made using ASRH on the heavy rain over the Jianghuai area,Henan and Shanxi region in June, July 2003. The results showed that the area and development of rainstorm is closed relevant with the big value center and evolution of average storm-relative helicity.When the correspondence of the upper and lower level ASRH is very well, some causality existed between the change of ASRH and the evolvement of heavy rain. ASRH perhaps is one of the mechanism of development of Meso-scale system.