Selenium(Se) is a kind of trace element in the soil and has three biological functions, that is, as nutrient, toxin and detoxin, it enters the food chain through plants, which absorb Se from the soil. So the content of Se in food depends on the content of Se in the soil, Se content in the soil is governed by a series of geological and geographical factors, while Se concentration in the plant is closely related to species of the plant per se and the environment it grows in. It is, therefore, essential to study soil selenium content. Content and distribution of Soil selenium is an important factor affecting yield and quality of the grain crops in the Northeast China Plain. Surveys and investigations in the past show that the Northeast China Plain is seriously in deficiency of soil and hence a region where endemic diseases prevail because of selenium deficiency. During the period from 2003 to 2006, a Multi-Purpose Regional Geochemical Survey (MPRGS) was performed in the Northeast China Plain, collecting soil samples from the surface (0~20 cm) and deep (150~180 cm) soil layers, 1 sample every 4km² and 1 every 16 km², respectively, for statistic analysis of distribution of soil selenium in the Northeast China Plain and its affecting factors. Results of the analysis show that the content of soil selenium in surface soil of the plain is lower than the average of the country, and its distribution is characterized by a rising trend from the salinized and desertified plain in the west to the low mound-hill region in the east, and strips of selenium-deficient soil and potential selenium-deficient soil alongside the river. About 51.54% of the plain in area is sufficient, 22.63%, potentially deficient, 25.05%, deficient and only less than 1% abundant in soil Se. In deep soils, soil Se content is very low and soils deficient in Se accounts for 80.68% in area. Soil Se content in the surface soil varies significantly with type of soil and pattern of landuse, and does not inherit much from soil parent rock (or deep soil). So the Se content in the surface soil demonstrates an apparent feature of enrichment relative to the content in the deep soil. The soils with apparent Se enrichment amount to 89.01% in area, and the soils depleted in Se are distributed mainly alongside the Songhua River. Correlation analysis shows that clay minerals, ferromanganese oxide and organic matter tend to adsorb Se thus enriching soil Se. Soil selenium enrichment is also quite obvious in farmlands, urban land and lands under some other land use. All the findings show that soil physicochemical properties and recent human activities are the main factors leading to Se enrichment in the soil, but the effects are far from adequate to make the surface soil abundant in selenium. It is, therefore, necessary to rationalize utilization of the land resources in the light of the above characteristics of soil Se distribution, control soil salinization and desertification, and reasonably adjust agricultural planting structure, so as to mitigate the stress of selenium deficiency and the incidence of Se-deficiency caused endemic diseases.