Abstract: The multi-purpose regional geochemical survey showed that the concentration of selenium in acid soil in Southern China is generally high, but the bio-availability of selenium in soil is relatively low, which affects the usage of selenium-rich soil. The pH values of soils are an important factor affecting the bio-availability. Se-rich red soil samples with pH of 3.91-4.98 and Se-rich paddy soil samples with pH of 4.33-5.75 were collected from Fujian Province and Hainan Island. Six experiments were conducted using lime and coal slag as the modifier to improve the bio-availability of selenium in soil. The results show that soil pH can be significantly elevated by 1 to 2 units by using the modifiers, which advances the mobility of Se in soils and improves selenium bio-availability in soils. Coalcinder and 10 times weights of quicklime have the same effect to promote selenium availability. The coalcinder as a regulation material is more economical and practical. It can not only realize the effective utilization of cinder, but also improve the soil structure and increase the soil selenium availability.