The invention discloses an experimental device for simulating the crystallizing of a karst tunnel drain pipe. A main water tank is arranged on a bracket; a first auxiliary water tank is arranged on one side of the main water tank in a length direction, and a second auxiliary water tank is arranged on the other side; the first auxiliary water tank is connected to the main water tank through a firstdrainage unit, and the second auxiliary water tank is connected to the main water tank through a second drainage unit; the first drainage unit and the second drainage unit are arranged on an adjustment bracket mounted on the ground; one side of the width direction of the main water tank is connected to the second auxiliary water tank through a water pump installed on a water supply pipe; the water pump is electrically connected to a control unit; and one side of the width direction of the main water tank is connected to the first auxiliary water tank and the second auxiliary water tank through water return pipes. The experimental device for simulating the crystallizing of the karst tunnel drain pipe disclosed by the invention has comprehensive influence factors, small volume and convenient operation, and can be popularized and applied to the technical field of karst tunnel drain pipe crystallizing research.