Abstract: Detail drainage analysis seriously influences evaluation of agricultural water resource in the Yinnan Irrigation District. According to the salt leaching requirement, transformation process of irrigation-drainage and feasibility of water saving, water saving potential of rice field was estimated and analyzed. Because of the difference in salt leaching effect between surface and subsurface drainage, the estimation method of irrigation drainage is different. Existing and relative steady deep subsurface drainage supplies a certain leaching capacity, and ditch drainage only needs to supply the shortage part. The results show that the deep subsurface drainage provids 182 mm leaching water, and leaching fraction is 0.16. Compared with the critical value of leaching fraction 0.31, or leaching depth of 343 mm required for the area, only 161 mm additional leaching water is needed. For the current rice growing area of 22333 hm² and ditch drainage volume of 445 mm, 284 mm may be reduced. In addition to the surface runoff of 309 mm, the potential of water saving from rice fields is 593 mm, or 132 million m³ in total volume, which is equivalent to 294 million m³ reduction in irrigation diversion from the Yellow River considering a canal conveyance efficiency of 0.45 in the Yinnan Irrigation District.