The present invention discloses a method for preparing graphene-polyamide nanocomposite fiber. The method includes the following steps of: mixing polyamide chips with graphene or modified graphene, and then extruding and palletizing to obtain graphene-polyamide masterbatch; melt-spinning the graphene-polyamide masterbatch after drying the same, to prepare the graphene-polyamide nanocomposite fiber. Compared with the existing industrial polyamide composite fiber, the method of the present invention has the advantages of simple process and low cost, and can effectively improve the production efficiency and capacity; the modified graphene has such an excellent compatibility with the matrix that it can be uniformly dispersed in the matrix, so that the graphene reinforced phase is perfectly compounded with the polyamide matrix material, thereby greatly improving the performance of graphene-polyamide nanocomposite fiber.