An analysis of weather process of a local heavy-hard rain which happened on October 3, 2008 in Ejina Banner, Inner Mongolia was conducted in the research. Firstly, the eastward movement of short wave trough and then combined with south branch trough was the necessary condition of the heavy-hard rain. Secondly, the combination and superposition of high cold trough, upward motion and vortex convergence area were the advantages for formation and development of medium scale and small scale systems. Thirdly, heavy-hard rain always happens in the environment with deep aqueous vapor layer, moisture convergence and strong-sustained ascending motion. In the forming region of upper-level divergence and low level convergence, convection developed, and the strong vortex convergence triggered the discharge of unstable energy, therefore, induced the happening of heavy-hard rain. Finally, the overlay of 700 hPa warm tongue and high cold trough induced the formation of wide thunderstorm belt.