This paper based on a 2-speed automatic transmission developing for an electric vehicle. Studied gear geometry modification impacts on electric powertrain NVH performance. Used analysis software to create ‘motor housing-motor rotor-transmission shafts and gears-transmission housing’ rigid-flexible coupling model. Simulated and analyzed transmission error, gear surface stress and vibration response. Extracted transmission bearings vibration data as excitation resource, simulated radiation noise in acoustic analysis software. The final results showed that at 9000 rpm, 84N•m torque with 1 meter distance, the calculated noise value decreased 1-2dB, which demonstrated gear modification has a positive effect on improving electric powertrain NVH performance.