Development and research on electric vehicles in power transmission system are increasing as the demand for ecofriendly and autonomous vehicles increases across the industry. In order to reduce noise, research on high efficiency and low noise due to electrification of the gearbox system is being actively conducted, such as applying design technology to optimize the shape of the gear and increase rigidity. In particular, research on low noise is active because the noise of the electric gearbox could be easily recognized in a vehicle, even with small noise due to its frequency characteristics. Therefore, in this study, effects of main specifications of gears on noise and power loss were studied and analyzed through a Parametric Study. Characteristics of the proportional relationship between noise and power loss according to major specifications were analyzed. Based on study results, NVH analysis in the gear system was performed. After that, actual data were secured through test measurements and a noise reduction effect of 4.4 dB was confirmed.