Abstract: Taking Lou soil as the research object, two typical areas of Zhouzhi-Huxian middle-acid soil and Sanyuan-Yanliang alkaline soil were selected. Wheat root soil and wheat grain samples were collected to analyze the selenium content in the sample and the selenium form in the soil. The effects of the change of pH value in soil on the selenium content, selenium form and selenium bioavailability in soil were as follows:(1) The pH had no significant effect on the content of Se in Guanzhong Lou soil, and the soil selenium form was strongly organically combined. The residual state and the humic acid binding state are mainly greater than 80%. The proportion of water-soluble selenium and ion-exchanged selenium is more than 10% in alkaline soil, 4.91% in neutral soil, 8.17% in weakly acidic soil, being "valley type". (2) Effective selenium, pH value is water soluble. The effect of selenium is not significant, and the effect on selenium content in ion exchange state is significant. (3) Compared with Qinghai, Ningxia and other regions rich in selenium,the selenium content of Lou soil in Zhouzhi-Huxian and Sanyuan-Yanliangareas is relatively low. However, the selenium enrichment rate of wheat grown in Sanyuan-Yanliang weakly alkaline and alkaline Lou soil is 89% and 100% respectively, indicating selenium organisms is higher under alkaline soil conditions, especially in weakly alkaline Lou soil.