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The objective of this study was to determine how different afforestation strategies and slope positions affect soil organic carbon and total nitrogen. In a unique steepland formerly used as farmland in the Yangjuangou watershed of the Loess Plateau, three adjacent afforestation transects were selected as the sampling site: two single-species transects (Hippophae rhammoides and Artemisia capillaris), which each represented the single-species afforestation mode, and one mixed-species transect, which represented the multi-species afforestation mode. The results indicated that: (1) The soil organic carbon concentration in the multi-species afforestation mode was 25.8% and 27.7% higher than that in the other two single-species afforestation modes, while a minute difference in total nitrogen concentration was detected among the three afforestation transects. (2) Within the mixed-species and Hippophae rhammoides transect, both the soil organic carbon and total nitrogen concentrations showed an increasing trend from the upper slope position to the foot slope position. However, the soil organic carbon in the Artemisia capillaris transect was higher in the foot slope and upper slope but lower in the middle slope, demonstrating a “V” shape, and the total nitrogen increased from the foot slope position to the upper slope position. (3) The carbon : nitrogen ratios were no more than 10:1, which indicated the presence of easily decomposable soil organic matter. This study demonstrated the multi-species afforestation mode has better carbon accumulation potential compared with the single-species afforestation mode, which has important and informative implications for future vegetation restoration practices in the Loess Plateau and similar semi-arid environments. [ABSTRACT FROM AUTHOR]