We demonstrate theoretically the existence of unidirectional surface plasmons in the nonreciprocal graphene-based gyrotropic interfaces. We show that a unidirectional frequency range is raised under a static external magnetic field where only one propagating direction is allowed for the surface plasmons mode. By efficiently controlling the chemical potential of graphene, the unidirectional working frequency can be continuously tunable from THz to nearinfrared and even visible. Particularly, the

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... unidirectional frequency bandwidth can be 1-2 orders of magnitude larger than that in metal under the same magnetic field, which arises from the superiority of extremely small effective electron mass in graphene. Based on our theoretical analysis, two tunable graphenebased directional devices are proposed, showing the appealing properties of nonreciprocal graphene in the nonreciprocal optical devices design. 6