Abstract: Experiment on rain harvesting under dry farming was conducted to determine the effects of ridge/furrow width ratio and mulching modes on soil moisture, soil bulk density and porosity in Medicago sativa cultivation fields. Based on the study, average water loss in the 0~120 cm soil layer was lower by 28.43 mm for plastic film covered ridges and 13.61 mm for compacted bare soil ridges than CK (flat field). The increase rate of rain water storage was 59.03%~99.27% in plastic film covered ridges with runoff generation efficiency of 53.43%~91.72% during the whole rainy season. From early April to early June (when was prior to 2009 rainfall collection period), the increase rate of rain water storage in compacted bare soil ridges was 1.92%~2.74% with corresponding runoff generation efficiencies of 1.71%~2.55%. From mid June to late September (when was mid-to-late rainfall collection period), the increase rate of rain water storage (8.85%~36.77%) and runoff generation efficiency (8.01%~35.82%) increased significantly. The increase rate of rain water storage and runoff generation efficiency on both plastic-film covered and soil-compacted ridges increased with increasing ridge surface area. However, increment in the increase rate of rain water storage and runoff generation efficiency on plastic-film covered ridges was remarkably higher than that on compacted bare soil ridges. Soil bulk density in the 0~40 cm soil layer significantly dropped in ridge/furrow rain harvesting system. The degree of drop in soil bulk density in plastic film covered ridges was higher than that in compacted bare soil ridges in the 0~20 cm soil layer. Accordingly, soil porosity in the 0~40 cm soil layer significantly increased in ridge/furrow rain harvesting system. Also the degree of rise in soil porosity in plastic film covered ridges was larger than that in compacted bare ridges in the 0~20 cm soil layer.