Taking acount of the latent heat of the vapour condensation in the atmosphere,the concept of the wet Q vector was proposed. An expression of the wet Q vector and the non geostrophic ω equation,in which the divergence of wet Q vector was taken as a forcing term,was derived. By using routine meteorological data for diagnostric analysis,the results show that the wet Q vector is better than the quasi geostrophic Q vector in the low latitude area.