The intrinsic vulnerability of karst groundwater source in the Qingmuguan karst valley is assessed quantitatively with the modified Slovenia model on condition of considering four factors: surficial material (O), runoff (C) and rainfall (P) as well as karst development (K). The results prove that high vulnerable area accounts for 12.6% of the total acreage, middle vulnerable area for 43%, and low vulnerable area for 44.4% in the watershed. It is high vulnerable area in sinkholes with their surrounding 100 m area. But most areas are middle vulnerable, and sandstone area is low vulnerable.