Abstract: Expansive soil is a kind of widely distributed and hard treated trouble soil. Slope failure may often occur in expansive soil. The best slope protection method of expansive soil slope can only be found, if the failure mechanism is considered. Existing research results of slope failure mechanism for expansive soil is summarized in this paper, and the special slope failure mechanism distinguished expansive soil from common cohesive soil is proposed, which is the crack developed in expansive soil, so special attention should be paid to it. The protection mechanism of expansive soil slope is analyzed, which is controlling slope soil water and limiting crack development. According to the difference in protection mechanism, existing expansive soil slope protection methods can be classified to two categories:limiting crack developing methods and non-limiting crack developing methods. The former includes geomembrane method, replacement method, chemical modified method and so on. The latter includes supporting structure method, surface protection method, soilbag method, physical improvement method and so on. Specific analysis and comparison is made for expansive soil slope protection methods, which can be as a reference in engineering application. In the end, suggestions are proposed for slope protection methods designing of expansive soil.