The invention provides a balancing system of a gantry double-stand-column machine tool. The gantry double-stand-column machine tool is provided with a gantry frame and a work unit, the gantry frame is provided with a first stand column, a second stand column and a gantry cross beam, and the work unit comprises a first stand column work unit and a second stand column work unit. The balancing system of the gantry double-stand-column machine tool comprises a first front spring, a first rear spring, a second front spring, a second rear spring, a first front pulley, a first rear pulley, a second front pulley, a second rear pulley, a first front hole, a first rear hole, a second front hole, a second rear hole, a front rope and a rear rope. After the first stand column work unit and the second stand column work unit are connected with the front rope and the rear rope through the first front spring and the first rear spring, the weight of the first stand column work unit and the second stand column work unit is balanced by the weight of the other work unit, and mutual assisting balance of the two stand column work units is achieved. The problems that the stand column work units of the gantry double-stand-column machine tool are large in weight, and the balancing system is complex can be solved, and meanwhile the balancing system is simple in structure and low in cost.