In this study, an effective polyethylenimine-crosslinked PVC electrospinning nanofiber (PEI/PVC-NF) adsorbent was developed to remove Reactive Black 5 (RB5) from water. FT-IR and FE-SEM analysis showed that PEI/PVC-NF was prepared successfully, and the desorption process under strongly alkaline conditions had a negligible effect on the nanofiber structure. The adsorption performance of RB5 on PEI/PVC-NF was evaluated using pH edge, adsorption kinetics, and adsorption isotherm studies. The results were as follows: the pH edge experiment revealed that PEI/PVC-NF has a high adsorption capacity for RB5 from pH 2 to 8. Kinetic experimental results demonstrated that the pseudo-first-order and the pseudo-second-order kinetic models described the adsorption of PEI/PVC-NF to low and high concentrations of RB5. The adsorption process was exothermic in isotherm studies, and the Langmuir model suited the data better. At 25 °C, the Langmuir model indicated that RB5 had a maximum adsorption capacity of 1,017.06 mg/g. Five repeated regeneration experiments proved its good reusability. PEI/PVC-NF is a prospective adsorbent for reactive dye removal because of its high adsorption capacity, rapid adsorption kinetics, easy separation, and acid and base resistance.