【Objective】Veterinary antibiotics are extensively used in livestock rearing industries all over the world for preventive and therapeutic treatments and growth promotion of poultry and/or animals. Antibiotics of the sulfonamide serial are commonly used in China, but once used, they are not so readily to be absorbed by the animals and are hence excreted along with feces and urine, which are often used as manure to build up soil fertility. After repeated application of the manure, sulfonamides therein tend to remain and accumulate in the soil and migrate from the soil into groundwater in certain environment. Long-term exposure to low concentrations of these antibiotics could be detrimental to non-target terrestrial and aquatic organisms. Therefore, investigation of the leaching behavior of these antibiotics in natural soils is the first logical step to assess their ecological risks and then develop corresponding pollution control strategies. 【Method】In this research, focus was laid on one of the widely used sulfonamides: sulfadiazine (SDZ), which is a compound slightly hydrophilic and low in adsorptivity in soils. Solute displacement experiments were performed to study migration processes of SDZ in undisturbed soil columns (Column I: 0~15 cm, and column II: 15~30 cm). Breakthrough curves (BTCs) of SDZ and tracer bromide were measured and modeled using numerical models that took into account reversible and irreversible kinetic sorption sites, as well as dynamic and stagnant area with the aid of the Hydrus-1D software. After calibration the numerical model was then used to predict and simulate residing and migrating behaviors of the substance in 200 cm soil columns relative to leaching velocity. 【Result】Results show that the BTCs in Soil Column Ⅱ were shifted to the left as compared with ColumnⅠ, which implied that, migration of SDZ was faster in the deeper soil layers. This is mainly due to changes in physical and chemical properties of the soil, such as humic acid content, cation exchange capacity and pH, with soil depth. The tested models all fitted the BTCs of SDZ and tracer bromide reasonably well. However, the TRM model which took into account dynamic and stagnant areas provided a better description of BTCs of SDZ than all the others did with R²> 0.91, RMSE < 0.061, f< 0.154, which indicates that the stagnant area is an important contributor to soil adsorption of SDZ. The predicted results show that when leaching velocities were the same, peak concentration of SDZ decreased and outflow lasted longer with soil depth. Measurements at the same depth show that with leaching velocity increasing from 0.017 cm min^-1 to 0.030 cm min^-1 and then to 0.100 cm min^-1, SDZ migration was accelerated, and SDZ concentration in the effluent increased too. When the leaching velocity was 0.100 cm min^-1, SDZ could quickly penetrate the soil profile and move into groundwater, and its breakthrough curve was no longer symmetrical, incurring a phenomenon of trailing. 【Conclusion】All the findings in this study may not only help improve knowledge of the mechanisms of retention and transport of the antibiotics in undisturbed water-saturated porous media, but also further demonstrate that the traditional solute transport model based on convection-dispersion-equation can accurately describe and predict the fate and transport of the antibiotics in soils.