In practice, the soils in shallow depth are usually subjected to the effect of wetting-drying cycles, leading to water content variations. As water content decreases, the dissolved salt starts to precipitate or crystallize, due to the saturation of salt in soil pore water. In reality, only dissolved salt has a significant effect on the thermo-hydro-mechanical behavior of salted soils, whereas the precipitated salt can be regarded as a soil solid. However, the existing description of salted soil compositions and salinity assessment do not take the salt state into account, thus limiting its application to salted soils that undergo significant water content changes. In this study, the description of salted soil compositions was revised considering both dissolved and precipitated salts. Then, the relationship between dissolved water salinity (the mass ratio of dissolved salt to salty water) and dissolved soil salinity (the mass ratio of dissolved salt to dry solid) was established. Considering the complex chemical compositions of soil pore water, the relationship between the electrical conductivity (EC) and water salinity (r) of mixed salt solution, which had the same salt compositions as synthetic seawater, was plotted to further transform the measured EC of soil pore water to water salinity. Salt quantity in both natural soils and salt-amended soils was determined by centrifuge and the EC-r relationship of the mixed salt solution, allowing water and soil salinity to be determined. Besides, the ion compositions and concentrations of soil pore water and site water were estimated by Inductively Coupled Plasma/Atomic Emission Spectroscopy. The similar ion compositions and concentrations obtained for soil pore water and site water proved that the adopted salinity assessment method was relevant. This was also confirmed by the results obtained on salt-amended soils with the measured salinities agreeing well with the target ones. Based on the obtained results, three approaches were proposed to determine the dissolved water salinity of salt-amended soils with decreasing salty water content. This allowed the dissolved soil salinity to be obtained according to the relationship between dissolved water salinity and dissolved soil salinity.