Purpose <p>This study aimed to evaluate the impact of straw mulch application rates under plastic film on soil water infiltration dynamics for optimizing water management in facility agriculture.</p> Methods <p>A laboratory soil-box experiment was conducted with four straw application rates (0.42, 0.8, 1.2, and 1.6&#xa0;kg/m²) and a control treatment (plastic film only). The dynamics of wetting front migration, cumulative infiltration, and infiltration rate were systematically analyzed. The infiltration process was simulated and evaluated using the Kostiakov and Philip models.</p> Results <p>(1) Straw mulching significantly altered water movement patterns, enhancing horizontal wetting front migration with increasing application rate (maximum 30.29&#xa0;cm at 1.6&#xa0;kg/m²), while optimizing vertical migration at 0.8&#xa0;kg/m² (28&#xa0;cm). (2) Cumulative infiltration exhibited significant suppression under mulching treatments, with the inhibitory effect intensifying progressively with application rate. (3) Initial infiltration rates were substantially reduced across all treatments, showing dose-dependent suppression within the first 5&#xa0;min, though these differences converged over time. (4) Both hydrological models demonstrated effective simulation of infiltration processes, with the Kostiakov model yielding superior accuracy for horizontal migration patterns.</p> Conclusions <p>This study confirms that straw mulching under plastic film serves to “promote horizontal movement and inhibit vertical infiltration” of water. Comprehensive analysis indicates that a straw application rate of 0.8&#xa0;kg/m² most effectively optimizes water distribution and is recommended as the optimal rate for water-saving regulation in facility cultivation. These findings provide a theoretical foundation for scientifically determining straw mulch rates in facility cultivation.</p>