We propose a method to realize the pulsed operation of all-fiber mid-infrared lasers. The absorption cross-section of dysprosium (Dy ³⁺) ions is overlapped with the emission cross-section of erbium (Er ³⁺) ions in fluoride glass in the 2.8 μm wavelength region. On this basis, a piece of Dy ³⁺-doped fluoride fiber is used as a fiber saturable absorber to achieve passively Q-switched pulsed operation at 2.8 μm in the all-fiber structure of an Er ³⁺-doped fluoride fiber laser. Furthermore, a pair of fiber gratings with a central wavelength of 3.1 μm are placed at both ends of the saturable absorber to solve the problem of passively Q-switching failure caused by the absorption saturation of Dy ³⁺ ions under high pump power due to the long lifetime of the upper energy level of Dy ³⁺ ions. A rate equation model for this 2.8 μm passively Q-switched Er ³⁺-doped fiber laser is built in view of this structure. The effects of the saturable absorber parameters and the resonator feedback conditions on the pulsed operation power and time characteristics of the 2.8 μm laser are evaluated. Numerical results indicate that the introduction of fiber gratings accelerates the recovery process of the saturable absorber, which is conducive to maintaining the Q-switched pulsed operation at high pump power.