Located in the capital inland arid area of north-west China, Changma irrigation region has poor natural environment.There is higher salt proportion in soils of plain region due to phrenetic water evaporation.About 80\^9% assart is salinized soil in Sulehe irrigation developing region, therefore the methods to improve salinized land and the influence to envoronment, especially the discharge area, caused by the change of water-salt balance call much attention of all society. Based on the observation data of soil's water-salt behaviors, six salt dynamic types can be classified: Salt Discharge, Salt Discharge In Irrigation Period, Salt Charge In Irrigation Period, Stable Type, Salt Dissolved In Irrigation Period, Salt Charge In Rain Period.The steady region of bad-soluble salt is in lower reaches of sulehe River, Anxi-Dunhuang Basin and Huahai Basin, instead of middle reaches of the river. Therefore the content of CaCO\-3 must be account when considering the total soluble saline and salt discharge design. By comparing three typical sites for leaching experiments of dissolvable salt of soil, the solution is that the effect wouldn′t be distinct if the total salinity was less chan 1-1\^5% (mean salt content of soils with in 0-100?cm in soil profile).
For different leaching types, deep drainage system is the most efficient method, and the effect is better for larger interval space of canals than that for sallow drainage system. All the conclusions can be regarded as the direct basis for project design and drainage administration by local government. Above all, a relation formula is produced between the rate of residual salt and quantity of accumulated leaking water,and the decision-maker can work out required water quantity according to primary salt content, so the scale of soil improvement can be confirmed matching the runoff of a river, in order to fulfill rational usages for water and land in primeval period of drainage basin development.