Abstract: The failures and slides of slopes of expansive soils are usually characterized by shallow sliding due to the fissures in the slope surface. The separation technology is to separate the external factors that cause their water change from the slopes, effectively prevent the fissure development induced by swelling and shrinkage, and thus effectively guarantee the stability of the slopes expansive soils. The soilbag protection technology is the typical separation method for the slopes of expansive soils, because the soilbage can effectively prevent moisture change from the slope surface. As a separation technology, the soilbag plays a role in separating the moisture change factors, restraining the swelling and strengthening the slope surface. The Rankine's earth pressure theory of expansive soils is presented according to the effects of swelling pressure. The design method of soilbags to protect slope failures of expansive soils is proposed for the protection of the slopes of expansive soils. The basic heap-up units of soilbags are constructed based on the application of soilbags to the cutting slope pretection of expansive soils in Chongzuo-Aidian highway of Guangxi Province. Therefore, the design method of soilbags to protect the slopes of expansive soils is proposed and standardized.