[Objective] The influence of overlying carbonate red soil on the infiltration characteristics of phosphogypsum was analyzed in order to provide an scientific basis for the rational disposal and utilization of phosphogypsum storage yards in southwest karst areas. [Methods] The influences of three phosphogypsum bulk densities (1.2, 1.3, 1.4 g/cm³) and three overburden thicknesses (0, 6, 12 cm) on the water infiltration process of phosphogypsum were studied through an indoor flat soil column infiltration test, and the infiltration process was numerically simulated using the improved layered Green-Ampt model. [Results] ① The difference in water infiltration time to the bottom between the 6 cm and 12 cm soil cover treatments was not significant (p>0.05). However, significant differences in infiltration time were observed between the 0 and 6 cm treatments, as well as between the 0 and 12 cm treatments (p<0.05). The initial infiltration rate, average infiltration rate, and stable infiltration rate of the 0 cm soil cover were significantly higher than those of the 6 and 12 cm soil cover (p<0.05), and the stable infiltration rate decreased significantly with the increase in soil cover thickness. There was no significant difference in cumulative infiltration between the 6 and 12 cm cover soil thicknesses (p>0.05), but there was a significant difference among the other cover soil thicknesses (p<0.05). ② For the same cover thickness, the influence of phosphogypsum bulk density on the initial infiltration rate, average infiltration rate, and stable infiltration rate was not significant (p>0.05). ③ The coefficient of determination (R²) between the measured and simulated values of the wetting peak depth varied was 0.951—0.995, the root mean square error (RMSE) ranged was 12.174—40.856, and the average absolute percentage error (MAPE) ranged was 0.070—0.227. When the soil was covered at 6 and 12 cm, the variation range of the determination coefficient (R²) between the measured and simulated values was 0.963—0.999, the root mean square error (RMSE) was 1.471—11.201, and the average absolute percentage error (MAPE) was 0.046—0.169. [Conclusion] There were significant differences in soil water infiltration characteristics between phosphogypsum-covered soil and uncovered soil, and the improved layered Green-Ampt model could be used to simulate the infiltration process of phosphogypsum under the condition of overlying soil.