During the roll forming factory, the front bearing of AC motor was always malfunction. The problem was that there was large axial vibration and the deterioration was in the trend of rapid development. In order to make early preparations for repairs and maintenance to determine the basis for decision-making, the motor bearings were under monitoring when running. In AC drive systems, bearings are more likely to be damaged from the highly accelerated/decelerated operation and the effects of electrical discharge machining resulting from high dv/dt, which are introduced by PWM input voltage. Multi-level inverters offer better sinusoidal voltage waveform than 2-level inverters due the fact that output voltage can be formed using more than two voltage level. This causes the THD to be lower. Switching losses are reduced because switching frequency can be lower than in 2-level inverter. According the testing data analysis, bearing had been replaced with 3-level AC inverter and maintenance of the response had been decided.