A heavy rainfall event in the eastern Fujian in 2002 is analyzed. The results show that helicity and CAPE are significant predictors to a heavy rainfall. The rainfall is generated where exist the positive helicity center at low-level and negative helicity center at high-level and high storage energy of potential instable at middle and low levels. The helicity is positive at upper levers and negative at low levels during the time of rainfall prosperity, and its maximum is at 700hPa. The high CAPE value is coincident with the center of the rainfall. The time and spatial variation of CAPE is well corresponding to that of rainfall. Based on the output of the mesoscale numerical model, the instable energy field is studied. It turns out that the release of potential instable energy may be one of mechanism for a heavy rainstorm genesis and development.