[Objective] The purpose of this study is to investigate the dynamic variation of soil water and salt in coastal saline-alkali area in Tianjin, and provide scientific basis for soil utilization and forest planting.[Methods] We took the Robinia pseudoacacia soil in Dagang district of Tianjin City as a case study, to study the annual variation of soil water and salt and salt ions distribution characteristics in different soil layers.[Results] The annual soil water content varied from 11.9%~28.8%, while salt content varied from 4.2%~18.4%. In spring(March to May) and autumn(September to November), soil water content was the lowest while salt content was the highest. Soil salt content increased with the increase of soil depth. Soil pH value ranged from 7.37 to 8.39. The content of K⁺, Na⁺, Ca²⁺, Mg²⁺ and Cl^- was the highest in the top layer(0-10 cm) in spring, and it was 0.04, 4.27, 2.69, 1.04 and 10.03 g/kg, respectively. Except for SO₄^2- and HCO₃^-, the coefficient variation of salt ions(29.99~162.98) in spring was greater than that in summer(2.87~88.13).[Conclusion] Soil water and salt content in different soil layers show an obvious seasonal variation along with local rainfall. Soil in the study area belongs to alkaline soil, and there is no significant seasonal change in soil pH value. Variations in K⁺, Na⁺, Ca²⁺, Mg²⁺ and Cl^- are consistent with soil salt content, while there is no significant seasonal variation in SO₄^2- and HCO₃^-. The distribution of salt ions is extremely uneven in spring.