There is high salt content in soil in the coastal tidal flat reclamation area of Jiangsu Province. In order to make rational use of rainfall and adopt underground pipe drainage facilities to improve the desalinization of soil in the tidal flat, an underground pipe drainage experiment was carried out in a typical area. By conducting tests under different underground pipe spacings, the analysis of soil’s salt content at different depths (0-80 cm) in the experimental area was carried out to study the dynamic change pattern of salinity in the soil profile. The results show that in the control area without underground pipes, the salt content of the soil at different depths shows an upward trend, while in the area with underground pipes, the salt content of the soil at different depths shows a general downward trend. Under different underground pipe spacing, the variation of the soil’s salt content at different depths is roughly the same, but the amplitude is different. A smaller underground pipe spacing indicates a more obvious soil desalinization effect; when the underground pipe spacing is the same, the soil desalinization effect will weaken as the depth of the soil layer increases.