A branch gully of Liudaogou watershed in the wind-water erosion crisscross region of the northern Loess Plateau was selected as the object, and the effects of slope aspects and plant community types on soil organic carbon (SOC), total nitrogen (TN) content, ratio of carbon-nitrogen (C/N) and soil organic carbon and nitrogen density (SOCD, TND) were studied through vegetation survey and sampling analysis. The results showed that:(1) Slope aspects had significant effects on the SOC and TN contents in 0-20 cm, and C/N in 0-60 cm. The SOC, TN contents and C/N followed the order of semi-shady slope > semi-sunny slope > gully-head, semi-shady slope > semi-sunny slope=gully-head, and semi-sunny slope > semi-shady slope ≥ gully-head, respectively. (2) Plant communities had significant effects on the SOC and TN contents in 0-10 cm and C/N in 0-20 cm. There was no significant difference in SOC and TN contents between three kinds of leguminous communities growing in the semi-shady slope, namely, Lespedeza davurica, alfalfa and sweet clover, but they were significantly higher than that of the Stipa bungeana community. The SOC and TN contents in Lespedeza davurica and alfalfa communities were similar in the semi-sunny slope, which were significantly higher than those of the Artemisia capillaris and Stipa bungeana communities. The SOC and TN contents in Lespedeza davurica community were significantly higher than that of the Stipa bungeana community in the gully-head, indicating that legume herb was more conducive to the accumulation of soil carbon and nitrogen in the study area. (3) Slope aspects mainly affected the SOCD and TND in surface layer of 0-20 cm, and their contribution to SOCD and TND of 60 cm soil profile were 45%~55% and 47%~53%, respectively. There were significant differences in SOCD and TND between the surface layer and the whole soil profile under different plant community types. The average SOCD in the studied branch gully was estimated to be 2.13 kg/m², which was far lower than other parts of the Loess Plateau. These results had important role in evaluating soil carbon and nitrogen storage accurately and rational construction of vegetation in the crisscross area of wind-water erosion on the Loess Plateau.