Abstract: Based on the first snow data from 16 weather stations in the western Tarim Basin from 1961to 2020,ERA5 reanalysis data,Global Data Assimilation System（GDAS） analysis data and conventional meteorological data,the climatic characteristics of the first snow in the western Tarim Basin in the past 60 years are analyzed.The large-scale abnormal circulation background,500 hPa circulation configuration,water vapor characteristics,and differences are researched in rain and snow conversion mechanism of the snowstorm in the western part of the Tarim Basin by taking the strong first snow weather from November 20-22,2020 as an example.The results show that the first snow in the western plain of the Tarim Basin has changed steadily in the past 60 years,and the first snow in mountainous areas has a significant delay trend.The strong first snow occurs under the abnormal“+-+”large-scale circulation at mid latitudes and the 500 hPa typical“east-west attack”situation.The deep Central Asian low vortex provides favorable water vapor conditions for snowstorm.The contraction and dynamic uplift of the terrain in the western part of the Tarim Basin,and the coupling of high-lowlevel jets provide strong dynamic conditions for the snowstorm.During the snowstorm,the high-level water vapor is mainly from the humid atmospheres of the European continent,Western Siberia,and Central Asia,while the low-level mainly comes from the return water vapor carried by the atmosphere inside the basin.The differences in low-level environmental humidity,boundary layer temperature advection,and cloud properties are the main reasons for the difference in the snowstorm weather.The high-cloud snowfall with dry low-level environment are more conducive to solid precipitation.The temperature of 850 h Pa ＜0 ℃ can be used as an indicator for this blizzard weather conversion of rain and snow in the western southern Xinjiang.