Abstract:By using the conventional observation and NCEP reanalysis data, this paper studied the wide range rainstorm which took place in Fujian Province on Oct. 5-6, 2008. It has been concluded that under the combined influence of the tropical depression trough and the cold air, low-level cyclonic convergence strengthened and the movement in the rainstorm area;the stronger vorticity advection at higher-level can promote the ascending movement; the stronger vertically differential advection of temperature results in the development of symmetric instability; generating and maintaining of longitudinal indirect secondary circulation promotes the intensity and duration of precipitation. The south currents at lower levels of the Southern China Sea provides water vapor continuously and creates the condition of dynamics and thermodynamics for the rainstorm area,at the same time it plays the key role in the progress of the unstable energy accumulating, transporting and releasing. Unstable stratification in rainstorm area maintained for a long time , and the vertical wind shear provided kinetic energy for the convection system development which is beneficial to the slantwise development of convection cells and inspired unsteady energy to release. The diagnosis ability of helicity in the tropical depression center, development and movement is better than the single factor of vertical velocity or vorticity, but it lagged behind the precipitation center.