In the present paper, based on the ultraviolet-visible (UV-Vis) absorption spectroscopy, fluorescence spectroscopy, and stopped flow-fluorescence spectroscopy, the authors studied the protein unfolding process of hemoglobin induced by GdmHcl. The experiments result shows that there were two different procedures about GdmHcl inducing hemoglobin unfolding from the evidences of UV-Vis absorption spectrum and fluorescence phase diagrams. Namely, the hemoglobin subunit exhibits depolymerization, forming the intermediates when incubated with GdmHcl at the concentration of 1.0 mol·L-1. With the increase in the concentration, various subunit structure became loose gradually, and the protoheme collapsed eventually. UV-Vis absorption spectroscopy indicates that the addition of reductant can cooperate with the depolymerization of hemoglobin subunit and the disaggregation of protoheme. The reductant results in the unfolding procedure that hemoglobin from “three-state model” turns into “two-state model”.