In order to investigate the mechanical behavior of steel reinforcing bars (rebars) after corrosion fatigue, axial tensile tests of rebars which were removed from corroded reinforced concrete (RC) beams after fatigue loading tests was carried out. Combined with the experimentally obtained stress-strain curves of the rebars after corrosion fatigue, constitutive relation model for the rebar after corrosion fatigue was quantitatively presented. And the model was verified by comparing the calculated values with the test ones. Test results show that, after cyclic loading to 2 million times, uncorroded rebars have the same ductile failure characteristics as the original ones without corrosion fatigue. Fatigue effect has no substantial influence on mechanical behavior of uncorroded rebars. Stress-strain curves for the rebars after corrosion fatigue changed obviously:characteristics of yield plateau changed, percentage of elongation shortened and yield strength decreased. The magnitude of variation correlated with the degree of corrosion fatigue. Mild steel changed into hard steel to varying degrees. The emergence of fatigue crack in rebar caused tensile failure in very low percentage of elongation, great reduction of yield strength and almost complete loss of ductility.