This paper establishes the theoretical model of 3.5 μm-Er∶ZBALN fiber laser and fiber amplifier using dual-wavelength pumping (DWP) technology. The kinetic behavior of the energy level particle number for the laser oscillator and amplifier and the laser power distribution along the fiber length under different fiber parameters are investigated. The effects of fiber length, output reflectivity, and erbium-doping concentration on the 3.5 μm laser power are calculated and analyzed. The results show that an optimal range of fiber length and output reflectivity. High erbium-doped fibers require only a lower 976 nm pump power compared to low erbium-doping to achieve an effective 3.5 μm laser output. The cross-relaxation process of high doped concentration prevents the quenching behavior. Simulations achieve an efficient amplification of the 3.5 μm fiber laser. The numerical simulation results are instructive for the 3.5 μm laser oscillator parameter design and high power amplification.