The invention relates to a chemical dissolution and cleaning dredging method for crystallization blockage of a karst tunnel drainage system. The problems that blockage of the drainage system by karstcrystallization universally exists in tunnel engineering in karst areas, and a serious threat to safety and long-term operation of a tunnel engineering structure is brought are solved. According to the chemical dissolution and cleaning dredging method for crystallization blockage of the karst tunnel drainage system, a polymer carboxylic acid type organic acid reagent with the concentration of 2000-2200 ppm and the dichromate index of 17.71-20% is adopted as a dissolution and cleaning solvent. The chemical dissolution and cleaning dredging method comprises the construction steps of electromagnetic detection of blockage points, arrangement of dissolution and cleaning pipelines, a chemical dissolution phase, auxiliary dredging measures, a cycle cleaning stage, and blockage of dissolution andcleaning pipeline holes. The dissolution and cleaning solvent is environmentally friendly, does not react with cement-based and PVC plastic materials, and can effectively clear karst crystal substances of the drainage system. The construction method can effectively solve the problem of blockage of the drainage system by karst crystallization universally existing in tunnel engineering in the karstareas.