This paper deals with the natural-conditions of Dayuzhang irrigation area in Shandong Province, the experiment of undlergrownd drainagre for improving saline soils in these area's, the observations and analysis of its effect and. the suitable condition of underground drainage. The experiment was eanductrd from 1978 to 1984. The results obtained indicated that the underground drainage could davain off the water and salt from soil, lower ground water table, increase the ratio of drainage to exaporation of the soil, speed up desatination of soil and ground water, intrease the yeeid of crops.and coon, avoid, the sliding of slopes of open ditch on silty soil. It is considered that undergroutad drainage hs an effectuie way to improve saline soil in coastal regions.