The invention provides a method for setting a salt elimination system through a closed conduit with an external-wrapped filtering layer made of fluidized bed furnace slag. The method comprises the following steps of: using a corrugated plastic pipe with holes as the closed conduit for salt elimination, using permeable non-woven fabric to wrap the external wall of the pipe to form a pre-wrapping pipe, digging a groove in the salinized soil, and selecting the fluidized bed furnace slag as the externally-wrapped filter material for salt elimination closed conduit; firstly laying the fluidized bed furnace slag at the bottom of the groove, then placing the pre-wrapping pipe at the position of the central axis of the groove, continuing to fill with the filter material until the filter material exceeds the top of the pipe to form an externally-wrapped filtering layer with the thickness of 10-20cm, then backfilling and tamping the salinized soil, and finally covering a layer of new soil on the top. Cross sections of the closed conduit salt elimination system from top to bottom are a plant layer, a new soil layer, a salinized soil layer, the externally wrapped material and a closed conduit layer. Main purposes of the invention are to protect natural resources such as gravel and to develop the technology and the technical measures that the solid waste furnace slag is used as the externally-wrapped filtering layer of the water/salt elimination closed conduit. The method provided by the invention has extensive application value in prevention and treatment, improvement and utilization of severe salinization and secondary salinization in coastal regions.