4.3 μm mid-infrared fiber lasers are produced by pumping Dy-doped InF3 with dual wavelengths of 1.7 μm and 2.3 μm. The spatial distributions of pump light power, signal light power and population density in the cavity are calculated, and the influences of pump light power, reflectivity of the output mirror, fiber length, and fiber loss on output laser power are numerically analyzed. The calculation results show that the self-termination effect can be effectively eliminated by dual-wavelength pumping, and the 4.3 μm laser output can be realized. The laser output power mainly depends on the power of 2.3 μm pump laser. When the 1.7 μm pump laser power is fixed, the laser output power increases linearly with the increase of the 2.3 μm pump laser power. When the 2.3 μm pump laser power is fixed, the optimal 1.7 μm pump laser power is obtained, which makes the laser output power maximum. The study results provide a feasible scheme for the operation of a 4 μm high-power continuous-wave fiber laser, which is instructive for obtaining 4 μm lasers via dual-wavelength pumped Dy∶InF3 fiber laser.