In order to explore the improvement effect of salinized soil and the impact of environmental pollution on the process of farmland drainage in Hetao Irrigation District, a typical branch canal irrigation control area was selected in the Hetao Irrigation District Urad Irrigation Area subsurface drainage comprehensive experimental area from 2019 to 2020. Systematic experiments were carried out on the hydrological process, the transformation, migration and collection process of pollutants during each crop irrigation period. The results showed that the DRAINMOD model can better simulate farmland drainage. The relative error (RE) between the simulated value and the measured value was 4.12%~13.44%, the correlation coefficient (R) was 0.80~0.92, and the efficiency coefficient (NS) was 0.82~0.90, all within the error range. The drainage process of bucket ditch and branch ditch is calculated by using Muskingen method and on this basis, the migration, transformation and pooling processes of NH+4, NO-3, reducing substance and salinity were analyzed. The simulation results of the drainage process and the concentrations of NH+4, NO-3, reducing substance and salinity were in good agreement with the measured values, indicating that this method can macroscopically describe the environmental pollution process formed by different drainage components in the irrigation area. The total emissions of main pollutants in the test area was reducing substance, NO-3 and NH+4, in descending order, which were 349.47~363.10kg,80.56~87.79kg, and 6.79~7.18kg, respectively. After two years of irrigation and leaching, the soil desalination rate was decreased from top to bottom in the soil. The soil desalination rate of the 0~20cm soil in the dark pipe drainage test area was 67.56%, which was 5.12 and 16.84 percentage points higher than those of 20~40cm and 40~100cm, respectively; 40~100cm were 12.90 and 15.58 percentage points higher respectively.After leaching, the soil salinity was changed from the surface accumulation type to the uniform type, and the soil EC values of the concealed pipe drainage and the open ditch drainage were between 2.20~2.63dS/m and 0.61~0.65dS/m after the autumn irrigation of 2020. The areas of moderately salinized soil and saline soil types in the experimental area were decreased, the area of moderately salinized soil was decreased by 2.94 percentage points, and the area of saline soil was decreased by 29.42 percentage points. Non-saline soil, lightly and severely salinized soil increased by 2.94, 8.83 and 20.59 percentage points, respectively. Saline soil contributed the most to the soil desalination rate in the experimental area, which was 126.77%.