The exposed karst areas has the characteristics of strong karst development and complex hydrogeological conditions， which leads to the concealed nature of the channels in underground river systems and the challenges for pollution prevention. Taking pollution prevention project in Pingqiao Underground River System as an example， the measure of “underground impermeable curtain + sewage pumping and drainage” was used in the main flow channels near the pollution source to realize “near source drainage truncation”.The construction faced difficulties such as blockages and low drilling efficiency due to complex karst fragmentation and excessive waste of materials due to long grout flow distances in strong karst segments. Effective technical measures such as suitable drilling techniques， pure pressure grouting， cement mortar grouting to fill dissolution voids， low-pressure and limitated volume grouting and accelerated slurry grouting were employed to ensure the quality of the project， which achieved the goal of contaminated groundwater treatment from the source. The technology of “near source drainage truncation” provides a replicable geoscientific management model for contaminated groundwater prevention in analogous hydrogeological conditions.