Abstract: Based on data of FNL 1 °× 1 °reanalysis data and conventional data,the mechanism of two rare warm snowstorms from 4 to 8 on January（The process Ⅰ）and from 2 to 6 on December（The process Ⅱ）in northern Xinjiang were compared and analyzed. The results show that the steepness structure of θ_se front,conditional symmetric instability and vertical circulation were the main dynamic mechanisms for the formation during the two snowstorms. The water vapor was the whole layer in the western boundary,and the lower troposphere was the strong convergence area of water vapor. The snowstorm area had warm and humid structure.The differences of two snowstorms were as follows:Firstly,the influence system of process Ⅰ was the low vortex type,while process Ⅱ was the short wave trough type.The duration of snowstorm in process Ⅰ was long,while the duration of process Ⅱ was short. The high and low troposphere configuration was also different between process Ⅰ and process Ⅱ. Secondly,during the eastward transport of Atlantic water vapor,process Ⅰ was supplemented by water vapor from the Persian Gulf and the Arabian Sea water vapor. Thirdly,the formation time and center of the conditional symmetric instability zone were different. process Ⅰ was formed 6 h before the snowstorm,and the center was located at 750 hPa,while process Ⅱ was formed 12 h before the snowstorm,and the center was located between 800 hPa and the boundary layer.The steep structure of θ_se front area in Process Ⅱ maintained longer and stronger than that of process Ⅰ.