Abstract: Farmland drainage works play an active role in preventing water-logging disasters, promoting crop growth, improving the management of farming fields. Reasonable drainage works may reduce or eliminate the impact of water-logging disasters, and it is the main way to increase crop production. DRAINMOD model can be used in the water table management system to simulate the subsurface drain flow and crop yield. Based in the datum of Shajiang black soil, weather, crops, and other information measured in the Huaibei Plain, DRAINMOD model was run for a long sequence in the simulation of crop yields for different drain spacing. The results show that the effect of spacing of drainage ditches on winter wheat’s relative yield is smaller. In the period of cotton growing, the probability of water-logging more than 50 percent, if the drainage ditches distance greater than 40 m, the relative yield of cotton declined significantly. In order to guide the design of drainage works, the design parameters of underground drainage system in this area should be designed according to the cotton’s design index.