Optical properties of 3.8-nm CuInS₂  /  ZnS core/shell quantum dot-doped optical fiber (CIS/ZnS QD-doped OF) were theoretically investigated as a function of fiber length, doping concentration, and pump power. The two-energy level system-based rate equations and power propagation equations were used to calculate the emission properties of QDs doped in the fiber. The emission spectra of CIS/ZnS QD-doped OF showed higher stability than the performance of the control sample doped with PbSe QDs under the same calculation parameters, which was confirmed by the smaller redshift rate as the fiber length increased. In addition, the maximal emission intensity of CIS/ZnS QD-doped OF was about five times that of PbSe QD-doped OF. Further, the light emitted by CIS/ZnS QDs could propagate in the fiber core for long distance with less reabsorption. The theoretical calculations fitted well with the experimental data in the literature. We provide a theoretical basis for CIS/ZnS QDs to be used as OF dopants to improve the fiber emission.