Abstract: A constant-head injection test with wetting front observation is conducted to investigate the effect of coal mining subsidence on infiltration into unsaturated soils in sand drift areas. The test is done on two subsidence sites that are formed in 2004 and 2005, and the two sites are located in the Bulianta mining area of southeast Mu Us Sandy Land. Results show that towards the end of the observation period (0-175 min), bigger distances of wetting fronts can be observed at many lowland locations with a sustainable infiltration capacity compared to that of observations on soil slopes. At the 2004 subsidence site with no cracks, both mean vertical infiltration rate and 175-minute infiltration depth are significantly larger than that of observations on the corresponding soil slope (P<0.05) in a control area. The same is true for the mean lateral seepage rate at the 2005 subsidence site with no cracks. At the subsidence sites, the vertical infiltration rate increases during the first ten minutes of the test in lowland locations, and then decreases afterwards. The rate increase can be found during most of the test time on soil slopes. While for the lateral seepage infiltration rate, such an increase is found during the first ten to twelve minutes and followed by a decrease afterwards. The rate increase can also be found during most of the test time on soil slopes. The factor analysis reveals a high vertical inflation rate at lowland locations, and the same is true for the lateral seepage rate on soil slopes. The findings can be seen as the main infiltration characteristics of unsaturated soils in sand drift areas.