Abstract: Long-term soil salt accumulation could lead to salinization. Aimed to prevent soil salinization, we investigated soil salt dynamics, its interface with the groundwater table, rainfalls duration and the impact periods when salt is mostly accumulated. Total soil salt accumulation and dynamic distribution were monitored in the 0–80 cm layer in alluvial farmland from 2018 to 2020. We found soil salt contents increased by 0.15 g kg–1 and 0.07 g kg–1 in the 0–40 and 40–80 cm soil layers, respectively, which indicated that soil salinization occurred. We defined the rainstorm impact period (RIP) as period when soil salt dynamic distribution was affected by rainstorm event. The salinity time-trend during RIP was sequentially characterized by a first salt leaching, followed by a rapid and then slow salt accumulation, which took the first 4 days, from day 4 to 10, and then beyond, respectively. In the first leaching stage, salt migration content was determined by rainfall (P < 0.05) which could leach 41.5% of salt on average in the whole soil layer. In the rapid accumulation stage, lots of salt accumulated due to high evapotranspiration and shallow groundwater table. In the slow accumulation stage, salt accumulation rate was inhibited by deeper groundwater table. In addition, the total accumulated soil salt in the whole soil layer increased by 0.14 g kg–1 in the RIPs, which comprised only 14.5% of the overall study period, but the value accounted for 63.6% of the salt accumulation, thereby indicating that RIPs were the main periods when salt accumulated during the soil salinization process. Our results provided insights into soil salt dynamic distribution during RIPs, thereby facilitating the effective prevention and control of soil salinization.