Abstract: Objective To study the effect of slope aspect on the community characteristics of mountain steppe and to reveal the change rule of plant community in different growing seasons.Method The mountain steppe in the northern slope of Tianshan Mountain was chosen as the research object,and the method of field investigation and sampling were used,and grassland community characteristics in the different slopes (the east slope,the west slope and the slope crest) and different growth period (June,July,August and September)were measured.Result (1) The important value of Artemisiafrigida in the whole growing season showed the slope crest ＞ the east slope ＞ the west slope;The important value of Stipa capillata in the slope crest and the west slope was significantly higher than that of east slope by 67.1;-673.7; (P ＜0.05);and the important value of Carex turkestanica in June and July showed the east slope ≥ the west slope ＞ the slope crest.(2) The community coverage of east slope in June,August and September was significantly higher than that of the slope crest and the west slope 21.4;-36.1; (P ＜0.05),and the community density in August and September was significantly higher than that of thewest slope,but the community aboveground biomass in July was higher than that of the west slope.Conclusion The slope and the growing season play important role in the community characteristics of mountain steppe Tianshan Mountains.