This paper studied effects of dryland terrace and crop types on soil organic carbon density in the watershed in north-ern semi-arid area. It provided theoretical guidance for reasonable farming and ecological safety in small watershed. 25 sample plot and 125 soil profiles in Dawujia small watershed in Aohan county of Chifeng in Inner Mongolia were selected in this study. The following results were obtained: (1) Soil organic carbon density for maize, sorghum, millet and mung bean decreased with soil depth and then increased, the maximum soil carbon density was in the depth of 50 ~ 100 cm; (2) The soil organic carbon density for all the four kinds of crops were reached the maximum at the elevation of 400 ~ 500 m areas, followed by an altitude of more than 600 m, and it was the lowest at the elevation of 500 ~ 600 m region; (3) The maximum soil organic car-bon density of four kinds of crops was in the areas of 2 ~ 6°, and the minimum soil organic carbon density was in the areas of≤2°; (4) In the level of P < 0. 05, the soil organic carbon density for four kinds of crops changed different in different slope. Soil organic carbon density for maize and millet showed a trend of south slope > north slope > west slope > east slope, and the sorghum and mung bean the trend was north slope > south slope > west slope > east slope; (5) The soil organic carbon density of mung bean was higher than other crops, with an average soil organic carbon density of 0. 81 g·cm - 2 .%针对北方半干旱地区小流域内旱地梯田的地形因子以及农作物类型对土壤有机碳密度的影响进行了研究，为合理地保障农作物生产和维持小流域的生态安全提供理论依据。试验地点在敖汉旗大五家流域，在流域内选取样地25块，共计125个土壤剖面，主要针对地形因子和农作物类型来分析其对土壤有机碳密度的影响，并得出以下结论：(1)玉米、高粱、谷子和绿豆4种作物的土壤有机碳密度随土壤深度的增加呈先下降再上升的趋势，在50~100 cm 深度时土壤有机碳密度最大；(2)玉米、高粱、谷子和绿豆4种作物的土壤有机碳密度在不同的海拔高度表现不同，海拔为400~500 m 时土壤碳密度最大，其次为海拔≥600 m 的区域，海拔为500~600 m 的区域最小；(3)玉米、高粱、谷子和绿豆4种作物的土壤有机碳密度随坡度的增大均呈现先下降后升高的趋势，坡度≤2°时土壤有机碳密度最小，在坡度为2~6°时最大；(4)在 p <0．05水平下，玉米、高粱、谷子和绿豆4种作物的土壤有机碳密度在不同坡向表现不同，谷子和玉米为南坡>北坡>西坡>东坡，而高粱和绿豆则为北坡>南坡>西坡>东坡；(5)玉米、高粱、谷子和绿豆4种作物中，绿豆的有机碳密度高于其他3种作物，平均土壤有机碳密度为0．81 g·cm -2。
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