Abstract: The Kumtag Desert，China’s sixth largest desert，lies in the south-east of the Lop Nur region，and is famous for the unique dune type of Pseudo-feathery dunes in the whole world. It is expanding and threatening to engulf previously productive lands with its arid wasteland character with the eastward speed of 1-4 m agely. The Tamarix sand-hillocks are one kind of special biological landform types，with legible age layers structure composited by sand and plant litters，in the Kumtag Desert. And their age layers structure was important significance to reveal desert environmental evolution. The paper applied age layers environmental analysis techniques to collect the grain-size sample of three typical Tamarix sand-hillocks in the Kumtag Desert，and the sand-grain characteristics of the age layers were analyzed for discussion the sedimentary environment evolution in the past 120 years. The results suggest as follows：（1）The Tamarix sand-hillocks’granularity composition of grain-size is dominated by the fine sand，whose age layer average content is 67.0 % and the content of coarse sand and coarse powder sand came next，with average value of 13.0% and 12.4%. They are every fine grain-size，badly sorted，a positive or very positive skewness，and a medium and narrow kurtosis，they belongs to aeolian sediments.（2）On the spatial distribution of grain-size，the sediments of the wetlands sand-hillocks in the east is every fine with content of sands accounting for 77.2% and average grain-size value of 2.99 Φ，the valley sand-hillocks in the west is every thick with sands content of 85.1% and average grain-size ranges of 2.92 Φ. On the other hand，the more increased the sedimentation age，the coarser the grain-size of age layers of the Tamarix sand-hillocks in the 20th century，the content of sands is minimum of the top sand-hillocks which changes from 61.7% to 78.8% and its bottom’s one is more whose sand content changes from 84.54% to 97.78%. It reflects the diversity changes of the sedimentation environment in the different habitats and deposition time.（3）The grain-size of age layers of the Tamarix sand-hillocks in the past 120 years reflects that the Kumtag Desert environment is mainly based on the dry-windy climate model and the obviously alternation process of drying and wetting are accompanied with it.

Key words: the Kumtag Desert, the Tamarix sand-hillocks, age layers, grain-size characteristics, sedimentary environment