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In China, there are large challenges for agricultural drainage system because of frequent flood and shortage of cultivated land, and new requirements are put forward to agricultural drainage system. Improved subsurface drainage was proposed which had characteristics of less cultivated land occupied, more environment friendly and larger drainage discharges than those of conventional subsurface drainage. Based on soil column experiment, the performance and mechanism of the improved subsurface drainage were analyzed under conditions of soil saturation and stable ponding surface water, which considered different soil textures, outflow conditions and ponding depths. Furthermore, a theoretical formula of improved subsurface drainage discharge was given. The results indicated that the drainage capability of the improved subsurface drainage was increased significantly. The drainage discharge equaled to 2~3 times of that of conventional subsurface drainage when filter width was varied from 2cm to 6cm under the experimental conditions. Drainage capability was increased with the increase of filter width, but the increased value was decreased gradually. In addition, the performance of improved subsurface drainage was going to be more obvious with the increase of gap between hydraulic conductivities of soil and filter. Compared the theoretical values with experimental ones, it was shown that the proposed theoretical formula was reasonable and feasible. The research results can provide technological support for the application of improved subsurface drainage. Meanwhile, the research will be beneficial to enrich theory and technology of agriculture drainage, which has important practical significance to ensure food safety and promote sustainable development of irrigated area.