With diabatic heating completely considered and based on a primitive equation,derived are an expression of modified ageostrophic wet Q-vector(Q^q) and the ageostrophic ω equation with the Q^q divergence as a forcing term.The modified ageostrophic wet Q-vector is then applied to diagnoses a heavy rain event.The results show that:the ability of simultaneously reflecting precipitation of Q^q is enhanced significantly in contrast to Yue Caijun's modified wet Q-vector(QM),original ageostrophic wet Qvector(Q^*) and ageostrophic Q-vector(Q^#);throughout the Meiyu front rainstorm process,the convergence intensity and center of 500 hPa Q^q divergence field are good indicators for the intensity and location of precipitation;and the vertical distribution of Q^q reveals the direction and intensity of the secondary circulation,and the heavy rain may occur around the uprising leg of the secondary circulation.