Abstract: By measuring water characteristic curve of sand and gravel of alluvial-pluvial fan of Yongding River in Beijing,the unsaturated hydraulic parameters including conductivity,specific water capacity and diffusivity were estimated,and the relationship between matrix potential and these parameters were established.Comparison between the measured water content and the estimated one indicated that the formula established in this paper could be used to estimate the unsaturated hydraulic parameters of sand and gravel of alluvial-pluvial fan of Yongding River.These parameters are basic data for simulating groundwater movement and solute transport in Beijing City.