Selenium (Se) in plants is considered as the main source of selenium intake by human body, and most plants absorb Se from soils. Therefore, Se contents in soil directly affect Se content in food. In this study, farmland soils were studied in Ping'an area of Qinghai Province, and total Se contents in soils and Se speciation and valence states were determined by atomic fluorescence spectrometry. The distribution of total Se contents in farmland soils and its relationship with soil parent materials and soil types were studied. The results showed that total Se content ranged from 0.089 to 0.782 mg/kg with an average of 0.418 mg/kg, and 58% of soils belongs to Se-rich soils. Total Se content of cultivated light chestnut soil was the highest in the study area, with an average value of 0.574 mg/kg; while was the lowest in irrigated loess, with an average value of 0.293 mg/kg. Se content in red mudstone of Paleogene-Neogene period Xining group was the highest, with an average value of 0.82 mg/kg. Se enrichment in Se-rich soil in Ping'an area is mainly due to the weathering of red mudstone of Paleogene-Neogene period Xining group. Organic matter-bound Se is the main Se speciation in soils, and iron-manganese oxides-bound Se was the least. Se6+ was the main valence in soluble, exchangeable and carbonate-bound Se. Se content in Se-rich soil is suitable in Ping'an area, and it has a good prospect of exploitation and utilization due to the high potential in Se supply and less pollution from external environment.