We have prepared the graphene/MoS2 heterostructure by a hydrothermal method,and presented its nonlinear absorption parameters and application as a nonlinear optical modulator in the mid-infrared region.Using the nonlinear optical modulator,stable passively Q-switched operation of an Er3+-doped ZrF4-BaF2-LaF3-A1F3-NaF (ZBLAN) fiber laser at ~2.8 μm can be obtained.The Q-switched Er3+-doped ZBLAN fiber laser can yield per-pulse energy up to 2.2 μJ with the corresponding pulse width and pulse repetition rate of 1.9 μs and 45 kHz,respectively.Our results indicate that the graphene/MoS2 heterostructure can be a robust optical modulator for pulsed lasers in the mid-infrared spectral range.