In the karst rocky desertification region of southwestern China, the uneven distribution of seasonal rainfall, shallow soil layers, and poor soil water retention contribute to the scarcity of soil water resources, which poses a significant threat to agricultural production. The efficacy of biochar as a soil amendment for enhancing soil quality and various soil properties has been confirmed; however, there remains a lack of consensus regarding its impact on soil moisture. The objective of this study was to investigate the effects of biochar application on soil moisture dynamics and water retention in karst sloping cultivated land. Twelve monitoring plots (2 m x 1 m) were established on the experimental farm at the campus of Guizhou University. Two treatments (T1 = 30 t ha(- 1); T2 = 60 t ha(- 1)) and a control group (CK=0 t ha(- 1)) were implemented on slopes of 10 degrees and 20 degrees, respectively. Soil water content was monitored for each treatment from November 2021 to November 2022 under natural rainfall conditions. The results indicated that the addition of biochar decreased the soil water content in the surface layer but effectively increased the soil water content in the subsurface layer. At the 10 cm soil depth, the soil water content under the CK treatment was higher than that under the T1 and T2 treatments. However, at the 20 and 30 cm soil depths, the soil water content under the T1 and T2 treatments was higher than that under the CK treatment. The addition of biochar can alleviate the downward infiltration of water. The response lag time (RLT) and response duration time (RDT) of soil water content to rainfall followed the order of T2 > T1 > CK, while the mean water infiltration rate (Wmean) and maximum water infiltration rate (Wmax) followed CK>T1 > T2. As a result, the addition of biochar does not significantly (P > 0.05) increase soil water storage (SWS). Therefore, the application of biochar had little effect on soil water content during rainfall, but led to differences in water infiltration response to rainfall and changes in post-rainfall soil water dynamics.