Abstract: The current high-resolution (centimeter-level) research on the ice-water interface salinity dynamics in shallow lakes is still relatively scarce, especially regarding the salinity gradient between the ice layer and water in cold and arid regions. Therefore, this study collected a total of 240 ice and water samples in 5 cm layers at L15 point in Uliangsuhai Lake on January 4, January 17, January 31, February 5, February 15, February 22, March 4, and March 11, 2017, and analyzed the vertical distribution of ice-water salinity. The results indicate that the mean salinity of lake ice (0.14 psu) is lower than that of the underlying water (2.34 psu), with water salinity being 11.10-23.81 times higher than ice salinity. From January 4 to March 14, salinity within the ice gradually migrated downward through brine channels and accumulated in the sub-ice water, leading to a continuous increase in water salinity, which reached a peak of 2.72 psu on March 4. Ice salinity exhibited a decreasing trend from top to bottom, with an average vertical salinity gradient of 0.005 7 psu/cm (downward migration), whereas water salinity increased with depth, showing an average gradient of −0.012 7 psu/cm (upward migration). At the ice-water interface, the vertical migration gradient was the strongest, reaching −0.431 4 psu/cm. This pattern is primarily attributed to the downward migration of brine within the ice under gravitational forcing, as well as the influence of salinity release from bottom sediments into the water column. These findings provide a scientific basis for understanding ice–water salt transport mechanisms in lakes within cold and arid regions.