Abstract: In order to design reasonably irrigation and drainage engineering and improve saline soil effectively, and investigate effect of the drain spacing on desalination of soils, leaching experiments were carried out on drained coastal saline soils laid 3, 6 and 9 m spaced subsurface drains respectively. The results showed that, during the leaching stage the drainage discharges in three experimental plots were great early, then decreased and kept stable roughly several days later. The drain spacing was smaller, the greater the stable drainage discharge among three plots, and the drainage water salinity was greater also at the early stage of three times leaching. The same leaching water column, desalinization of soils in the plot with 3 m spaced subsurface drains was more uniform, and was not very uniform with 9 m spaced subsurface drains. After three times leaching, the desalinization rates of 0~1 m soil layer in the plots with 3, 6 and 9 m spaced drains were 70.93%~73.40%, 64.68%~77.47% and 56.54%~78.78% respectively. The equation was applicable to estimate soil salinity variation in the flooded and pipe-drained field, and the prediction error was a little more at the sites above drains, but was 10% or so at the other sites between drains.