Ping'an is a selenium (Se)-rich region located in northeastern Qinghai Province of China. To better understand the selenium geochemical distribution and its potential ecological effects, this field study investigated the Se distribution in the local environment, soil Se bioavailability, and the daily dietary Se intake of Ping'an residents. Concentrations of total Se were determined in soil, plant, water, and food samples. Results showed that Ping'an is generally a Se-rich region in China. High-Se soil mainly distributes in the north of Hongshuiquan Town in the study region. Se concentration in 43 plant samples varied significantly from not detected (nd) to 904 μg/kg, following a descending order of pasture > grain > vegetable > fruit, which was much lower than other regions in China. The drinking water Se concentrations were also significantly lower than the European and Chinese surface water Se standards of 10 and 50 μg/L. The predicted daily dietary Se intake (48 ± 20 μg per person) in Ping'an met the demand of the WHO-recommended Se amount of 55 μg per person. The Se content is high in soil, but low in different kinds of plants and Se intake, indicating that Se that can be taken up by plants was very low. The K2HPO4-KH2PO4-extractable Se in the soil accounted for only 3% of the total soil Se, indicating that a low soil bioavailable Se might result in low Se accumulation in plant tissues in Ping'an. This might be due to the influences of geochemistry and the inherent properties of the parent materials of these soils. Therefore, further studies need to focus on better understanding the process and influential factors to soil Se bioavailability to successfully utilize the soil Se resource in low-Se-availability areas.