【Objective】Reclaimed soil in an open-air coal mine is highly infertile due to its poor physical and chemical characteristics. The reclamation methods usually improve soil moisture content which has important theoretical and practical significance for the reclaimed mine soil.【Method】This experiment was conducted in the Heidaigou open-air coal mine in the Inner Mongolia Autonomous Region, in which the following treatments were applied; fly ash, arsenic sandstone and dump soil. A certain mass ratio gradient was set, including 13 blended treatments denoted as L3F1, L4F1, L5F1, L1S1, L2S1, L3S1, L4S1, L5S1, L1F1S1, L2F1S1, L3F1S1, L4F1S1, L5F1S1, in which the L, F, S represented three kinds of controlled treatments. The volumetric water content of each compound soil under different water suctions was measured by the centrifuge method for the drawing of the water characteristic curve using the Gardner fitting model. The specific water capacity, field water capacity, wilting coefficient and effective water content of each treatment were also calculated.【Result】The results showed that the Gardner model was appropriate to fit the water characteristic curves of the 13 compound soils. The addition of fly ash increased the content of fine soil particles (i.e., clay and silt) by 24.11% to 37.19%, respectively, and improved the water holding capacity and water supply of soil. Furthermore, the addition of arsenic sandstone improved the water holding capacity of soil but failed to improve the water supply performance. The water holding capacity of L1F1S1 treatment and water supply performance of L3F1 treatment was the best, which was 47.6% and 40.23% higher than that of the dump soil, respectively. The field water holding capacity and available water content of LF combined treatment and LFS combined treatment were enhanced with the increase of additive proportion. When the mass ratio of soil and fly ash in the dump was 3:1 (L3F1), the maximum field water holding capacity was 18.02%. On the other hand, the maximum available water content was 13.1% with the mass ratio of soil, fly ash and arsenic sandstone of 1:1:1 (L1F1S1).【Conclusion】Overall, the comprehensive utilization of fly ash and arsenic sandstone is beneficial to improve the soil water characteristics of coal mine dump, and the soil water holding capacity and water supply capacity is better when the clay and silt contents of the soil are within the range of 30%-35%. In this experiment, the mass ratio of 1:1:1 is the best.