Abstract: A three dimensional saturated-unsaturated numerical model was applied to the engineering problem of various saturated porous media with complex boundary condision.There was a flyash lagoon of thermal power plant in the mountain valley.The model domain with space of 1.1 km×1.0 km×72 m was large and quite irregular.In the numerical simulation,some conditions were taken into account,such as the rainfall infiltration,the drainage,the evaporation and the various water level of reservoir caused by the mountain torrents.In addition,using a series of tests and analysis,the water characteristic curve and unsaturated conductivity of the coal ash as a special engineering material were determined.