[Objective]The effect of seasonal freeze-thaw on soil micro-aggregates in the context of climate change was studied in order to provide references for the reserch of soil biochemical processes near the timberline.[Methods]Soil samples from three typical vegetation types(meadow,Larix principis-rupprechtii and Picea meyeri)near the timberline of Wutai Mountain were collected for soil column in situ experiment. Soil micro-aggregates contents and fractal dimensions(D)were measured.[Results]The variations of 2~0.25 mm and 0.25~0.05 mm aggregate contents were different among the three plots.The content of 0.05~0.02 mm aggregate reduced initially,then increased and finally reduced.The content of 0.02~0.002 mm aggregate reduced initially and then increased(except in Larix principis-rupprechtii plot),and the content of<0.002 mm micro-aggregates increased firstly and then reduced.The content of micro-aggregates changed significantly(p<0.05)due to seasonal freeze-thaw events in initial freezing and thawing periods,while there was no significant change in deep freezing period(p>0.05).Soil micro-aggregate contents also changed significantly (p< 0.05)in the growing season.Different vegetation compositions caused significant differences(p<0.05) among micro-aggregate contents in three plots,especially,in initial freezing and thawing periods.During the freezing-thawing period,Dvalues were increased,and that of Picea meyeri plots was the lowest.In growing season,Dvalues were decreased,and that of meadou plots was the lowest.Significant differences(p<0.05) of Dvalues among three researched plots were only observed in the late growing season,and the least D value is obtained in H.principis-rupprechtii.[Conclusion]Freeze-thaw cycles have great impacts on soil micro-aggregate contents.The responses of soil structures to seasonal freeze-thaw events are significantly different, and mainly occur in initial freezing period and thawing period.The D values of all plots are increased by freeze-thaw cycles.Although the D value of soil microaggregates increased during the incubation period,it gradually decreased to the pre-incubation level after entering the growing season.Soil aggregations and structures of all three plots vary periodically and have certain self-recovery capabilities.