Abstract: Assessment on the vulnerability of karst groundwater source is an effective measure for the protection and effective management of karst aquifer. In the most part of Southwest China karst area, the karst groundwater is liable to be contaminated for lack of proper protective zone for groundwater. 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 rain fall (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 surrounding100 m area. Sinking stream with its surrounding10 m area, and high karstified area are the high vulnerable areas. But most areas are middle vulnerable, and sandstone area is low vulnerable. The assessment is coincident with reality, which supplies simple and clear scientific basis for reasonable programming and protection of groundwater. The method in the paper is worth to be popularized in the field of the assessment on the vulnerability of karst groundwater source in the East Sichuan karst valley region.