Ten heavy rainfall processes，which caused severe flooding in Jilin and Liaoning Provinces of Northeast China, occurred during July to August in 2010. The total precipitation is characterized by frequent processes, large amount precipitation and colocated rainfall area. By using the observational data of surface, upperair, satellite, Doppler radar, regional AWS and the operational NWP analysis data of T639 and NCEP FNL, the causes for the above characteristics are presented. The main results are as follows: (1) The frequent rainfall processes are mainly caused by the convergence of westerly cold air flow and strong warm, moist southerly air flow, which are supported by a stable and abnormal general circulation. (2) The ten rainfall processes can be divided into two categories based on the most important upperair influence weather system, category one is about low vortex (including shear line) mainly occurring at low levels, category two is about cold vortex (including trough) mainly occurring at middle to higher levels. The circulation characteristics, water vapor source and the role of cold air are different for each category. (3) Case study of each category shows that the large amount precipitation is caused by the convective cells, which initiated at almost the same place and moved through the concerned place frequently. (4) The mechanism of cells initiated is different for two cases. The case “7.20” convective cells are initiated at the ascent and potential unstable zone of geostrophic deviation wind convergence and ahead of cold front aloft; the case “7.27” convective cells are mainly triggered by surface front. (5)The Corfidi vector method provided a good estimate of the motion of the most active elements of the convection system. The above results are valuble to heavy rainfall forecasting of the Northeast China. The analysis method can be also applied to the heavy rain forecasting of other places.