Squall lines which occurred in cold vortexes over Northeast China were analyzed by using data observed at the Harbin weather station and other data sets. The results show that ① The squall lines mostly occurred when the cold vortexes developed strongly and were over the front regions,which had thermodynamically unstable structure. ② There are basically three necessary conditions for the occurrence of squall lines,i.e. unstable thermodynamically structure,convergence of water vapor in the low levels and strong convection.③ A mesoscale weather system occurred near surface. ④ The synoptic scale kinetic energy was transferred to the mesoscale system when the squall lines enhanced.