Employing the data of a Meiyu front rainstorm during 5-6 July,1991 in the Changjiang-Huaihe Basins,as well as the surface precipitation distribution,the diagnostic characteristics of quasi-geostropic-,semi-geostrophic-,ageostrophic- and wet-Q-vector are analysed qualitatively(vector field) and quantitatively(divergence field).Results suggest that as far as the diagnostic function of quasi-geostropic-,semi-geostrophic-,ageostrophic- and wet-Q-vector are concerned,the second is superior to the first which is the worst of all,and the third and the last are advantageous over the first and the second obviously;ageostrophic-wet-Q-vector is almost the same with the wet-Q-vector on a qualitative basis,however,on a quantitative basis,the wet-Q-vector is the best of all;the diagnostic property of various Q-vectors at 700hPa is better than those at 850hPa and 500hPa in reflecting precipitation,especially,the convergence of the wet-Q-vector at 700hPa has a good relation with precipitation distribution.