A rainstorm process that occurred during 24-25 Jul 2011 is analyzed by numerical simulation performed with NCEP data used for the initial field. The numerical simulation accurately simulates this rainfall process and essentially reflects the rainfall distribution characteristics. The moist thermodynamic advection parameter is chosen to perform diagnostic analysis for the rainfall region. Results show that in the meridional-vertical cross section of the zonal mean of the moist thermodynamic advection parameter, the high-value areas, and the centers of the moist thermodynamic advection parameter coincide well with the heavy rainfall region and that the gradient and the upward height can qualitatively indicate the intensity. The vertical integral of the moist thermodynamic advection parameter can trace the heavy rainfall region more accurately than the light rainfall region. The centers of the moist thermodynamic advection parameter do not completely overlap the heavy rain centers; instead, the high-value areas of the gradient correspond to the centers. Moreover, the moist thermodynamic advection parameter has a spatial distribution and time evolution trend similar to those of the simulated 6 h accumulated precipitation, and its change trend can reflect the increase and decrease of precipitation.