Abstract: The study aimed to simulate soil moisture dynamics incorporating gully slope flow processes. The watershed was first discretized into a series of orthogonal grid cells. Then, a distributed rainfall-runoff model (Grid-XAJ-SS) considering slope gully flow mechanisms was developed. The model also accounted for channel flow movement emphasizing the lateral flow redistribution mechanism between adjacent grid cells along the slopes. The model was validated through multiple flood events （2014—2024） in the Wuqiangxi inter-basin watershed, showing runoff depth errors ranging from − 3.2% to 2% and peak flow relative errors between 2% and 5%. The simulated soil moisture distribution exhibited a correlation coefficient of 0.66 with precipitation patterns, whereas spatial variations exhibited a rank correlation coefficient of 0.47 as compared to those exhibited by LPRM AMSR2 satellite data. These results indicate that the Grid-XAJ-SS effectively simulated a high-precision runoff and elaborated the spatiotemporal dynamics of soil moisture. The simulated soil moisture patterns were physically consistent with rainfall distribution characteristics and spatially coherent with satellite-derived moisture observations.