Based on various conventional observations and the NCEP reanalysis data, the associated thermodynamics, dynamic mechanisms, instability mechanism and the features of satellite images for the occurrence and evolution of severe rainstorm caused by typhoon Bolaven (1215) and cold air in central Heilongjiang are analyzed. The results suggested that the severe rainstorm results from the interaction of middle and low latitude circulation systems. The southeastward advance of cold air greatly enhances the baroclinicity, in favor of the development of baroclinic disturbances. During this rain storm process, the co existing of instability in the low troposphere and moist symmetry instability in the middle troposphere provides a powerful ambient condition for the occurrence of this rainstorm. The positive vortex tube in the mid low layer of the atmosphere drives the development of convection. Strong convergence at low levels and divergence at high levels, and mesoscale circulation provides dynamic conditions. The southerly and southeast jet in the east side of typhoon center provides abundant moisture and thermodynamic conditions. In addition, the terrain helps to increase the intensity of the rainstorm as well.