In the construction of tunnels located in the dolomite area, the problems caused by the blockage of the drain pipe (ditch) crystallize one after another. The blockage of the drain pipe (ditch) is one of the potential factors for the leakage of water in the tunnel. Therefore, it is of great engineering significance to find out the factors and mechanisms of crystallization of the dolomite tunnel drainage system. In this paper, the crystallization mechanism and crystal characteristics of the mixed solution of dolomite tunnel drainage system are analyzed based on geological investigation, water quality testing, crystal structure, etc., the causes of crystalline blockage of drainage pipes are analyzed by combining indoor model tests and crystallization breaking tests, and finally, the optimization suggestions of the drainage system are proposed. The results show that the water samples of the dolomite tunnel drainage pipeline belong to the mixed solution of multi-ions, the cations are Ca2+, Mg2+, Al3+, etc., and the anions are CO32−、HCO3−、SO42−, etc. Among them, the mass fraction and concentration of Ca2+, Mg2+, Al3+ are relatively high., while the mass fraction and concentration range of Fe3+、Cu2+、Zn2+、Ba2+ are approximately 0; the crystal powder contains Cl, O, S, K, Ca, Mg, Al, Na and other elements, and the content of Ca, Mg, Al In comparison, Ca is more, Al is less, and Mg is between the two; after the evaluation of the degree of crystallization blockage, it is found that the degree of blockage of the transverse drain pipe per linear meter is higher, the circular drainage pipe is lower, and the longitudinal pipe is between the two. The crystal removal effect is more significant with the increase of the ultrasonic vibration frequency. It is found that the optimal removal frequency is 50 kHz, and the optimization suggestion of the drainage system is given in combination with the "V"-shaped pipeline arrangement.