Freshwater scarcity and soil salinization limit coastal agriculture, and brackish water irrigation may help alleviate regional water shortages. This study examined the effects of irrigation water salinity on water–salt dynamics and ion distribution in coastal saline soil from Laizhou Bay. Repacked soil column experiments were conducted using a freshwater control and brackish water treatments with TDS levels of 1, 3, and 5 g L⁻¹. Soil water content and electrical conductivity were monitored at 1 min intervals at five depths, and pore water ion composition was analyzed after infiltration. Higher salinity was associated with reduced cumulative infiltration and infiltration rates, delayed wetting front migration, and longer infiltration durations. Freshwater cumulative infiltration reached 11.94 L, whereas the 3 and 5 g L⁻¹ treatments decreased final cumulative infiltration by more than 11%. Soil EC increased with salinity, with higher values occurring mainly in the middle and lower soil layers. Na⁺ and Cl⁻ were the dominant ions contributing to salinity risk and moved downward with the wetting front. Low-salinity brackish water caused less short-term infiltration inhibition and salt accumulation risk than higher-salinity water under laboratory column conditions. However, field validation, crop response evaluation, economic feasibility assessment, and long-term salt balance analysis are required before practical irrigation recommendations can be made.