Abstract: With the method of immiscible displacement, the drainage and imbibition curves are accurately measured for a single joint in granite sample. The mechanism governing the unsaturated flow in the joint is discussed on the basis of the data obtained from the test. According to the probability distribution, an analytical model for the relationship between capillary pressure and saturation, and an expression for unsaturated hydraulic conductivity are put forward. The studies show that the unsaturated hydraulic conductivity of a single joint has certain similarities to that of porous media; the models proposed in this paper can be used as a reference method for deterimining the unsaturated seepage paramenters of rock joints.