A method for growing a graphene nanoribbon on an insulating substrate having a cleavage plane with atomic level flatness is provided, and belongs to the field of low-dimensional materials and new materials. The method includes the following steps. Step 1: Cleave an insulating substrate to obtain a cleavage plane with atomic level flatness, and prepare a single atomic layer step. Step 2: Directly grow a graphene nanoribbon on the insulating substrate having regular single atomic steps. In the method, a characteristic that nucleation energy of graphene on the atomic step is different from that on the flat cleavage plane is used, and conditions, such as the temperature, intensity of pressure and supersaturation degree of activated carbon atoms, are adjusted, so that the graphene grows only along a step edge into a graphene nanoribbon of an adjustable size. The method is mainly applied to the field of new-type graphene optoelectronic devices.