For the gear sets of wheel side reduction systems used in electric vehicles,a new lightweight design method based on road load spectrum is put forward.According to the standard road driving cycle,the computational load spectrum of gears generated by extrapolation methods generate gears and the gear fatigue strength characteristics,the reliability and durability of the gear sets can be analysed.Controlling variable method is used to have a good understanding of how the change of module of gear or the gear parameter influence reliability and durability of gear sets.Meeting the demands of driving mileage required,the lightweight optimization design of gear sets has been made.