975 nm and 1975 nm dual-wavelength pumped 3.5 μm Er∶ZLBAN fiber lasers have been numerically modeled. Laser power and particle density are estimated in both time and space dimensions and simulation results match well with the experimental reports. The whole process of stable continuous laser oscillation in a dual-wavelength pumped 3.5 μm Er∶ZBLAN fiber laser is showed by simulation. 3.5 μm laser characteristics are estimated and studied with different fiber parameters, such as pump power, 1975 nm pump mode overlap factor, reflectivity of output lens, and interionic interaction. The condition in which ESA₂ process has great influence on laser power is also investigated. Simulation promotes the understanding of 3.5 μm Er∶ZLBAN laser dynamics and provides valuable insight for laser designing.