【Objective】The key to achieving sustainable utilization of newly reclaimed cultivated land in coastal areas is to control the upward accumulation of soil salinization. In this context, mulching and subsoil interlayer placement are widely adopted measures to mitigate salt accumulation in the surface soil. However, the combined effect of straw mulching with a biochar interlayer on soil water and salt transport in the southeastern coastal regions remains unexplored.【Method】This study considered a newly reclaimed cultivated land in the coastal areas of Fujian Province as the research object, and explored the impacts of biochar salt-barrier layer (with burial depths of 25 cm and 45 cm) combined with straw mulching on the distribution of water and salt during the water infiltration and evaporation processes of saline soils.【Result】The results demonstrated that the incorporation of a biochar interlayer significantly decelerated the wetting front advancement during the leaching process. Among all treatments, T3-25 (straw mulching combined with a biochar interlayer at 25 cm depth) exhibited the most pronounced effect, reducing the migration distance by 4.07% compared to the control (CK) after 73 hours of infiltration. As the leaching time prolonged, the salt content of the leachate in all treatments gradually decreased. On the first day of leaching, the T3-45 treatment (surface straw mulching + 45 cm biochar interlayer) had the highest leachate salt content, reaching 16.24 g·L?1. In terms of total desalination amount, CK outperformed all interlayer treatments due to the absence of interlayer obstruction; it also had the highest pH value (8.07) after leaching. In the 0~45 cm soil layer, a significant reduction in soil salt content was observed across all treatments. The control (CK) treatment exhibited the highest desalination rate at 68.68%, while the T3-45 treatment demonstrated a superior desalination effect compared to T3-25. Regarding specific ions, the T3-25 treatment showed the most pronounced decrease in Na? content, with an average reduction of 74.76%. Also, under the evaporation condition with a groundwater table depth of 65 cm, the soil water content in the 0~45 cm layer was significantly higher in both T3-0(straw mulching only) and T3-45 treatments than in CK. Following 45 days of evaporation, a notable increase in both total salt and Na? content was detected in the 0~45 cm soil layer for all treatments. Additionally, the T3-45 treatment displayed the lowest increments in the salt accumulation rate and Na? content, at 3.49% and 14.06% respectively, relative to pre-evaporation levels. In contrast, the CK treatment exhibited the most severe salt accumulation, with corresponding increases of 54.21% and 150.19%. By the end of the evaporation stage, the soil pH in all treatments had increased significantly compared to both pre-evaporation values and the CK, with the relative increase over CK ranging from 0.71% to 3.57%.【Conclusion】Based on the experimental results, the combined application of straw mulching with a biochar interlayer at 45 cm depth proved most effective. It not only reduces water evaporation but also achieves the best performance in promoting desalination and inhibiting the salinization of coastal saline soil. This study found that the effects of the T3-25 treatment and the T3-45 treatment are similar. In practical applications where upfront cost-effectiveness is a consideration, the improvement measure of straw mulching with a biochar interlayer buried at a 25 cm depth can be considered for newly reclaimed coastal farmlands in the southeast region.