Abstract: Based on the invading conceptual model for unsaturated seepage of a single fracture, and considering fracture initial capillary pressure of drainage, fracture aperture range of drainage process, etc., a constitutive model for unsaturated seepage saturation, capillary pressure and relative permeability coefficient of a single fracture is derived, and the verification analysis of the model is done according to the experimental data. The study shows that the derived model for saturation and capillary pressure about a single fracture is in good agreement with the experimental results, and the relationship between saturation and relative permeability coefficient has good comparability with that of the classical model. Taking the disconnection condition of fracture, initial capillary pressure and the minimum and maximum aperture of drainage probability into consideration, the invading conceptual model will be in more accordance with the actual condition when pressure modified term is introduced. Finally, the unsaturated drainage process of a single fracture is simulated by use of software UDEC. The results are close to those of Van Genchten model, and the conclusion that the model is reasonable and reliable is drawn.