Abstract: Cracks are frequently observed in Xiashu soil, which have great infiltration capacity during rainfall and easily induce shallow landslides and other geohazards. In order to study the characteristics of rainfall infiltration of Xiashu soil, in this paper, the actively heated fiber Bragg grating(AH-FBG)method was used to perform field monitoring of moisture distributions and their variations in in-situ soil. Based on the monitoring results, the spatial and temporal distribution characteristics of volumetric water content in winter and summer were obtained, and the rainfall infiltration and recharge coefficient of rainfall events were calculated. On this basis, the permeability coefficients of Xiahu soil were estimated using the steady-state method, which were compared with those measured by the indirect method. The results show that the application of AH-FBG based in-situ monitoring of moisture in Xiashu soil is feasible. The root mean square error of 5 cm depth is larger and 0.0252 m³ ·m^-3. It is mainly affected by the heat exchange between the shallow soil and the air, as well as the soil cracks. The errors for other depths are not more than 0.01 m³ ·m^-3. The in-situ monitoring system has good responses to the change in water contents caused by rainfall infiltration and evaporation. Both in winter and summer, the in-situ unsaturated permeability coefficients calculated by the steady-state method are larger than those estimated by the indirect method, which indicates that the cracks in Xiashu soil provide a preferential seepage channel for rainfall infiltration.