The invention provides graphene modified spandex fiber as well as a preparation method and application thereof. The preparation method comprises the following steps: uniformly mixing a first part of graphene material and a chain extender in an organic solvent to obtain a chain extension solution; mixing diisocyanate, polyether glycol and a second part of graphene material for a pre-polymerization reaction; adding an organic solvent for dilution to obtain a prepolymer solution; mixing the chain extension solution with the prepolymer solution for chain extension to obtain a polymer solution; uniformly mixing a third part of graphene material with a dispersing agent in an organic solvent, adding the mixture into the polymer solution, curing and spinning, wherein the weight ratio of the graphene materials added in the three steps is (20 to 40):(10 to 30):(30 to 70). Compared with traditional spandex fiber, the spandex fiber provided by the invention has the advantages of high elongation at break, strong breaking strength, high electrical conductivity, high antibacterial rate and the like, and can be used for making underwear, ski suits, sport suits, swimming suits, welts, conveying belts, medical fabric, space suit, and the like.