Abstract: The leaching requirement for the Hetao Irrigation District of Inner Mongolia Autonomous Region, China, was estimated by numerical simulation. To simulate the salt transfer under leaching evaporation conditions, a modified solute transport model, Second Order model compared with Two Region model(SOTR), was employed. An advanced numerical method, the characteristics method combined with the finite element(CMCFE) scheme, was used. The simulation was verified by experiment of soil water transport in the soil column using a Gamma ray method. The salt transport processes were investigated when solutes leach and redistribute through a vertical homogeneous soil based on the soil water and solute dynamics. The relationship between the dynamic long term distributions of soil salt content and the leaching requirement, ground water depth, ground water salt concentration and initial soil salt content distribution in an arid area was discussed and analysed. And the optimum leaching requirement for the Hetao Irrigation District was determined.