Abstract: To study the shear strength characteristics of basalt fiber-reinforced clay, a series of direct shear tests on clay reinforced by dispersed basalt fiber are performed under controlled water content and dry density conditions. With the application of scanning electron microscope (SEM), the soil particles on shear surface are investigated at micro level. The ratio of fiber content to dry soil by weight is 0. 0%,0. 15%,0. 25% and 0. 35%. And the representative soil samples are selected from shear surface under stress of 400 kPa for micro tests. The experimental results show that the inclusion of basalt fiber in clay can enhance the cohesive stress of soil, which increases with the increasing fiber content. Compared with that of pure soil, the internal friction angle of basalt fiber-reinforced clay changes little when the content is not higher than 0.25%. But when the content reaches 0.35%, the internal friction angle increases abruptly. At micro level, the dispersion of fiber in soil is the highest when the content is 0.25%. The interfacial interaction between fiber and soil particles mainly includes gripping effect of single fiber and fiber-net effect. The fiber on the shear surface may be either slipped or broken during shear, which the breaking of basalt fiber is different from that of other fibers. The ends of fiber are mainly broken, while the surface is smooth.