The invention belongs to the technical field of graphene and provides a method for preparing a graphene nanoribbon with the width being 100-1000 nm in order to solve the problems that preparation of graphene nanoribbon at present is limited by the sizes of raw material carbon tubes and a wide graphene nanoribbon vapour deposition method is high in preparation cost. According to the method, linear nano carbon fibers serve as raw materials, the nano carbon fibers are first stripped through oxidation etching, then the oxidized graphene nanoribbon is purified, and finally the graphene nanoribbon is obtained through reduction. The preparation method is easy to operate, the number of the raw materials is large, the raw materials are low in price which is 1/3 that of the carbon tubes, and experimental dose production and industrial large-scale production of the graphene nanoribbon with the width larger than 100 nm can be achieved.