The MM5 model is used to simulate the heavy rain process occurred in August 2000 in Hebei Province.The results show that the process was caused by a cold vortex over the eastern Mongolia and the subtropical high,and the direct trigger for the local severe heavy rainfall was a mesoscale convective cloud cluster.There was rapid accumulation of energy before the mesoscale system took shape.Sensitive experiments on terrain effect and southeast winds at low levels for the heavy rainfall process are conducted.It is concluded that although the heavy rain occurred in the eastern Hebei Province,this process was greatly affected by the mountains over the west and north parts of North China.When the terrain is removed,the location and intensity of the heavy rainfall change obviously;and when the low-level southeast wind is weakened,the movement speed and intensity of the cold vortex over the eastern Mongolia change in different degrees;and the lower the level is,the more obvious the effect.