Reinforcement technology by geogrids has special effect for controlling geo-hazards occurred in expansive soils. But at present the research on the characteristics of interface between geogrids and expansive soils is insufficient; with laminated shear test apparatus, a series of pull-out tests is carried out to study the interaction between plastic uniaxial geogrid and expansive soils under different vertical loads. The soils are taken from the weathered expansive marlite in Xinxiang, the middle route of the South-to-North Water Transfer Project. The research results show that: the pull-out process of geogrid from expansive soils falls into three main stages, i.e. the interfacial static friction stage, progressive shear stage and the overall motion stage. There is obvious difference on the stress characteristics in each stage. As the normal stress increases, the ratio of the static friction to the interfacial shear strength shows a logarithmic increase, is from 0.20 at 50 kPa to 0.57 at 400 kPa; and its extreme value can reach 0.75. When adopting geogrid to reinforce retaining wall and high slope, the maximum static friction proportion should be considered; there is different vertical stress at vertical height of geogrid; sectional design is more reasonable.