Using 1 h rain data observed by AMS and NCEP/NCAR 1°×1° reanalysis data, according to circulation features of a typical case of cold vortex over Northeastern China, the process was divided into 3 phases which were called developing phase, mature phase and weakening phase, respectivly. The precipitation of developing phase was caused by moisture baroclinic instability on westerly frontal zone which belongs to regional mixing precipitation. The other precipitation phases were caused by convective instability, which was main convective rainfall. There is instable energy area within cold vortex in all phases, but it has obvious difference. The warm and moisture air transportations and convergences are key factor to the accumulation of instable energy, so the instable energy area is located in southeast of cold vortex far from center in developing phase, located in southeast of cold vortex near center in mature phase, and in weakening phase instable energy area is located in low trough which evolved from cold vortex. The instable energy brings different convective rainfall in different phases. CAPE and bigger vapor flux are the main elements to decide precipitation area in developing phase. Convective mainly occurs in overlapping area of CAPE and humid area in 925 hPa in mature phase. In weakening phase, convective is not only related to CAPE and relative humidity, but also to convergence line in lower troposphere.