A new method of modified optimization of double helical gears is proposed based on reducing vibration and noise and raising machining efficiency. Firstly, the straight profile of rack-cutter edge is replaced by three segment parabolas, and the equation of the rack-cutter profile is ultimately represented in the rack-cutter surface. Secondly, the physical and mathematical model of tooth contact analysis and loaded tooth contact analysis of double helical gears are introduced and then the loaded transmission errors are obtained. The optimal modification parameters are achieved based on the minimum amplitude of loaded transmission error. Finally, a set of equipment for measuring loaded transmission error, the analysis software platform and the test-bed of vibration and noise are designed, respectively. The feasibility of the method of modified optimization is verified. Compared with vibration and noise before modification, those after modification averagely decrease 18% and 2.7 dB.