Utilizing GDS unsaturated triaxial apparatus and pressure plate extractor, the tensile crack propagation depth of unsaturated expansive soils is studied. A linear elastic solution of the tensile crack propagation depth is presented and reduced coefficient of effective cohesion is defined. Expressions for critical matrix suction at the ground surface, and the crack propagation depth with no influence of the depth of the groundwater level are derived from the equation of crack propagation depth. Relationships with influencing factors are compared, such as effective cohesion, reduced coefficient of effective cohesion, effective internal friction angle, Poisson's ratio, matrix suction at the ground surface and the depth of the groundwater level. Based on above, the influences of tensile cracks on tension zone depth are analyzed, considering three typical matrix suction profiles along the depth, that is, constant, linear and parabolic distributions.