Abstract: Using the WRF model data, a heavy rainfall on August 16, 2013 in the northeast of Liaoning Province was analyzed in meso-scale for the dynamical and thermodynamic mechanism of genesis and development of a heavy rainfall. The results showed that: (1) the reason of the heavy rainfall was meso-β convective weather system, the “train effect” made the convective weather system following steering flow above lower atmosphere through northeast of Liaoning Province, that was the main reason of the flooding calamity; (2) the topographic force and positive vorticity advection divergence started the heavy rain; (3) the instable energy was deposited through the middle-level west cold dry airflow with low-level southwest warm humidity airflow, the vertical ascending motion and dynamical frontogenesis in the low level played a positive role in potential instability. Triggering mechanism of the latent instability was the ascending motion at the upper level.