Abstract: To study the effect of seawater irrigation on soil salinize-alkalization and saturated hydraulic conductivity, 75% seawater was applied to irrigate in field experimental plots in the seashore saline soil of Yellow River Delta in three years. The change of the soil salt content, index of soil salinize-alkalization and soil saturated hydraulic conductivity before and after seawater irrigation were analyzed. The results are as follows: the salt content increases in soil profiles after 75% seawater irrigation. The salt accumulation can be found below 80 cm of soil layers. The soil saturated hydraulic conductivity decreases after seawater irrigation. The pH values of soil and the residual sodium carbonate(RSC) do not change any more before and after seawater irrigation. Sodium-adsorption ratio(SAR) and exchangeable sodium percentage(ESP) of soil rise and surpass the critical value of alkali-affected soil after seawater irrigation in three years. SAR and ESP with the salt content of soil are in a good relationship with logarithm. Therefore, seawater irrigation can affect safety of soil resources in the Yellow River Delta. The secondary salinization and alkalization of soil must be prevented in the process of seawater irrigation.