Unsaturated hydraulic conductivity is a key parameter in unsaturated loess analysis, it is a function of matric suction or volumetric water content, but difficult to deternine which specific function relationship is. Moreover, the unsaturated hydraulic conductivity is difficult to measure, indirect deduction from soil water characteristic curve (SWCC) is more random, steady-state and indoor transient profile method require taking the soil disturbance into account. Under these circumstances, the in-situ transient profile method is adopted to process the natural rainfall infiltration monitoring data, the relationship between the unsaturated hydraulic conductivity and the volumetric water content of loess is obtained. In addition, based on the actual distribution of volumetric water content at different times, the relationship between the volumetric water content and depth is proposed by using a logarithmic curve, and applied to the data processing step of the transient profile method. The results of the in-situ transient profile method show that the relationship between the unsaturated hydraulic conductivity and the volumetric water content is an exponential function. Meanwhile, due to rapidly evaluating the unsaturated hydraulic conductivity in field, the method is introduced. The calculated results show that method has a high degree of agreement with in-situ transient profile method. On the other hand, the logarithmic curve is used to fit the relationship between the volumetric water content and depth when using the method; thus, one of the basic assumptions of the method is amended by the logarithmic curve relationship; and the results of the modified method are closer to the actual conditions.