Abstract: Considering diabatic heating is the most notable feature of moist Q vector, and the difference among moist Q vectors is caused by differing conductional methods of diabatic heating. Therefore, the comparison and analysis of diabatic heating can display the difference among diagnostic abilities of moist vectors. Typhoon Haitang landing Fujian Province from 0800 LST 19 July to 0800 LST 20 July in 2005, gives rise to wide range heavy rainfall in northeast of Fujiang Province and most of Zhejiang Province. The rainfall process is simulated successfully by the Weather Research and Forecasting (WRF) model .Combining a torrential rainfall process associated with landfalling typhoon Haitang (2005), using the simulated outputs from WRF model, and by calculating precipitation field, the role of diabatic heating and its influence on diagnostic ability of moist vector are analyzed quantitatively. The results are as follows: (1) As far as diabatic heating only including large-scale condensational heating and diabatic heating including latent heating (large-scale condensational heating and convective condensational heating), sensible heating and radiation heating are concerned, the forcing role of local variation term is about 1-2 order smaller than the counterparts of vertical advection term and horizontal advection term, which can be omitted, the forcing role of vertical advection term is the predominant component, and the forcing role of horizontal advection term is smaller than the counterpart of the vertical advection term evidently while larger than the counterpart of the local variation term obviously, which is contributed to depict the forcing roles of and completely. To diabatic heating only including latent heating in the non-uniformly saturated moist atmosphere, the forcing role of horizontal advection term is basically equal to the counterpart of vertical advection term, which are the primary components of , and the forcing role of local variation term is secondary whereas it can not be omitted, which is contributed to portray the forcing role of fully. (2) The 24 hours accumulated rain fields forced by roles of diabatic heating , and have similar horizontal distribution characteristics, and the hourly cumulative rainfall amounts forced by the three have similar time evolution features, which both disclose that vapor condensational latent heat plays the main role in the diabatic heating. (3) On the basis of the simulated precipitation field, the analysis shows that the precipitation fields forced by and are more close to the simulated precipitation field than the counterpart forced by , which displays that the diagnostic abilities between the moist Q vector including and the moist Q vector including are almost equivalent, and their reflecting abilities to precipitation are stronger than the counterpart of the moist Q vector including . (4) Each moist Q vector has its diagnostic characteristic, hence, according to the requirement of the research object, the corresponding moist Q vector can be chosen as the diagnostic tool with a clear aim. If the forcing role of vapor latent heating is needed to be considered carefully, the moist Q vector including or can be chosen. If only the total forcing role of moist Q vector is considered, the moist Q vector including can be chosen.