Abstract: Based on an investigation of the ground substrate layer of black soil region in Baoqing County, Sanjiang Plain, this study collected a total of 244 topsoil samples (0-20 cm) and 50 paired sets of crop grains and corresponding root-zone soils (including 7 sets of rice grains, 36 sets of maize grains, and 7 sets of soybean grains), and systematically analyzed the selenium(Se) content in different soil types and land use types, as well as in crop grains and the corresponding bioconcentration factors (BCF). The results indicate that the topsoil Se content in Baoqing County ranges from 0.09×10_-6 to 0.411×10_-6, with a background value of 0.239×10_-6. Soils with adequate Se account for 88.91% of the total area, while soils with potential selenium deficiency and Se-deficient soils together occupy 11.05%. Se-rich soils are limited to only 3.64 km², and no Se-toxic soils were identified. Among soil types, black soil showed the highest Se content, followed by meadow soil, albic soil, paddy soil, swamp soil, and dark brown soil, in descending order. In terms of land use types, water bodies exhibited the highest Se levels, succeeded by construction land, dry land, paddy field, and forest land. The average Se content was 0.054×10_-6 in rice grains, 0.027×10_-6 in maize grains, and 0.049×10_-6 in soybean grains. The mean Se BCF values were 0.081% for maize, 0.177% for rice, and 0.137% for soybean. Se enrichment was moderate in rice and soybean grains, but weak in maize grains.