A comparative diagnosis of the divergence and frontogenesis fields of the ageostrophic wet Qvector (Q*) and the improved ageostrophic wet Q vector (Qq) is made for a torrential rain process over the eastern QinghaiXizang Plateau occurred on 18 to 19 July 2005. The results show: (1) The convergence field of the Qq reflects the intensity and area of the heavy rainfall more precisely than that of Q*. The lowerlevel atmospheric forcing is the main driving factor of the vertical motion in the heavy rain area, which made the updraft accelerate under the instability stratification and caused strong convection. (2) The frontogenesis function of Qq with all diabatic heating effects reflects the center and area of the heavy rainfall more precisely and has stronger frontogenesis effect. After the rainfall, due to the release of instable energy, there appeared evident frontolysis.