The “Positioning abnormality” situation, that a wing shafts of gantry Numerical Control (NC) machine tools losing the gravity balance, has been reduced efficiently without replacing the main drive parts, for this a method is proposed. The mechanical transmission gap and slipping were the main reason according to exclusive analysis, for the wing shaft precision abnormality after emergency stop alarmed from a dual-driving wing shaft of one large type 5axis gantry NC machine tool. Base on the practical production and the waiting period of spare parts in one plant, the old component’s deflection was reduced through the precise assembly, and the dual drive parts transmission was optimized and synchronized to prolong the service life. Also the hydraulic balance time to gravitational compensation had been prolonged to make up for the wears error of used parts which were hard to eliminate in precise assembly, and finally reduced largely the influence of the problem to machine tools. There was no part accident happened, although 6 times emergency stop alarm occurred during 11 months continuously using, which proved the effectiveness above method. Machine’s function is recovered without replacing the traditional transmission old parts, and the old errors are compensated using hydraulic balance, which has strong practical value in using and maintenance.