Abstract: Using the WRF/ARW model to simulate a proceeding of cold vortex over Northeast China during 8－12 July 2007. The analysis of synoptic weather indicates that the cold air mass above the north of Lake Baikal moves to the cold vortex over Northeast China and enforces it. What is more, a part of the cold air transfers to the middle and lower troposphere from the tropopause, which causes the process of dry intrusion. Besides, in the east of cold vortex, there is the convergence of water vapor transport, which indicates the water vapor is plentiful there, and the intersection of the cold dry air and the warm wet air benefits the formulation of rainfall. The results of wind structure of mesoscale convective system (MCS) prove that the southeast and northeast parts of cold vortex, where there exists the maximum of cyclonic curvature, are the areas prone to MCS, which leads to the heavy rainfall. Finally, the vertical component of convective vorticity (CVV) is used to diagnose the location of MCS rainfall, and the corresponding of CVV and rainfall shows that CVV could indicate the area of rainfall.