The two-dimensional (2D) nanomaterial saturable absorber represented by graphene is widely used in ultrafast fiber lasers due to its unique nonlinear optical properties. In this paper, we summarize the research and development of 2D nanomaterials as saturable absorbers in mid-infrared ultrafast mode-locked fiber lasers in recent years, and introduce the atomic structure and nonlinear optical characteristics of 2D nanomaterials, and saturable absorber device integration methods. The laser performance parameters such as center wavelength, repetition frequency and average output power of the laser are discussed, and the femtosecond fiber laser based on black phosphorus saturable absorber in the middle infrared band is highlighted. Finally, the developments and challenges of 2D materials in mid-infrared pulsed fiber laser are also addressed.