Water resources security has been threatened by some factors,such as seasonal water shortage,frequently alternant waterlog and drought,and water pollution in karst area of southwest China because of particular environmental geology. Four parts of water resources security assessment are discussed in the paper,namely water quantity security assessment,water quality security assessment,water resources utilization security assessment,and water disaster security assessment. Finally,the countermeasures guaranteeing the security of karst water resources are clarified,including building water resources warning system,combined security assessment and management information system,economy revolution,protecting exploitation groundwater,optimizing water resources distribution,and accelerating ecosystem building,etc.