Abstract: In order to solve the blocking problem of the drainage system in karst tunnels caused by karst crystalliza? tion, the scanning electron microscopy and chemical analysis experiments are carried out to obtain the microstructure and chemical compositions of the karst crystals acquired in the drainage pipes of the karst tunnel. Then chemical compositions of solutions for scavenging the Karst crystals are studied, the experiments on the solution concentration and dissolution effect are performed to determine the optimal concentration of the cleaning solution on the basis of analyzing the relationship between the solution concentration and dissolution rate. The results indicates that the solution of the unimolecule carboxylic organic acids reagent or the polycarboxylic organic acids reagent with an optimal concentration of 2 000 ppm and a dichromate index of 17.71% can effectively remove the karst crystals in the drainage system under the premise of ensuring green and environmental protection.