Expansive soil is a special clay soil, possessing three features of swelling and shrinkage, over-consolidation and fissures. With the large-scale construction of high-class highway and fast development of the western regions of China, the hazard that expansive soil brings to construction and management of highway becomes more and more serious, so it is of significance to study on the slope problems of highway in the areas of expansive soil.Based on the survey of a section of xi'an-hanzhong freeway through expansive soil area, this paper studied on the characteristics of engineering mechanics and seepage flow of expansive soil slope on road-cutting by the four methods of laboratory tests, field survey, theoretical analysis and numerical simulation. Meanwhile, the theory of unsaturated soils mechanics was applied to expansive soil study. The main contents were briefly listed as follows.Firstly, laboratory tests were carried out to analyze clay mineral contents, disintegration character, swell-shrink character and the relationship among some indexes after field inspections and sampling of expansive soil along xi'an-hanzhong freeway, then the basic engineering characters were summarized.Secondly, the soil-water characteristic curve of undisturbed expansive soil was studied by using high-speed centrifuge. The soil-water characteristic curve with volume change was presented and density-change curve was described by Brooks-Corey model, then the modified-Kovacs model was developed to calculate the soil-water characteristic curve according to the primary parameters of expansive soil.Thirdly, field survey had been performed for six months by TRIME water measurement system and tensiometers on expansive soil slope. The influence of climate change on the suction and water content regulations was analyzed, and the depth of climate influence was calculated according to Mitchell equation.Fourthly, the expressions of initial cracking and cracking evolution of expansive soil were obtained based on the theories of lineal elastic mechanics and fracture mechanics, and the mechanics index influence on the cracking depth was clarified and the cracking depth were established theoretically.Finally, the properties of seepage flow and slope stability were analyzed according to unsaturated soil mechanics. Targeting to expansive soil fissures, a method of equivalent material was presented to simulate rainfall infiltration to slope so as to study on distribution of the water content and suction on expansive soil slope with fissures. This thesis analyzed the important influence to slope stability and verified the engineering examples, afterwards put forward some construction schemes and engineering methods about slope engineering problems of road-cutting.