Based on the data of FY-2E Stationary Meteorological Satellite from China Meteorological Agency(CMA), Doppler radar products, the reanalysis dataset from the NCEP/NCAR reanalysis project and convention observation, the caused mechanism of a rare snowstorm event in the west of southern Xinjiang was analyzed.The results show that the rare snowstorm occurred on the background of central Asia trough to south cutting cortex low.The favorable configuration of three jet streams in snowstorm is similar as in rainstorm.It is unusual that the low-level jet's speed exceeds 20 m·s^-1 in winter.The formation time of low-level jet earlier than the high-level jet 12 hours plays an important role in the snowstorm.Favorable configuration about the jet streams of higher southwest and lower east to provide the power and water condition for the snowstorm.Water vapor source payments calculation analyses show that there are three parts of water vapor sources, the first is thick central Asian vortex itself carry water vapor form southwest airflow, the second is by east of airflow water vapor concentration and convergence form southern basin on middle low level, the third is conveying the relay water vapor that warm-moist from the coastal margin of southeast China.The water vapor transmission from the east airflow is more than others.The two meso-β-scale cold clouds are the main systems for the severe snowstorm.The mesoscale cloud enhanced in local is the direct effect of heavy snow.The main radar echo during the snowstorm is stratiform cloud.In local place the radar echo intensity gradient is large and has the short-term weak convection characteristic.