Abstract: HRB600 high-strength steel bars have been included in the national standard of steel products in China and have been commercially produced. However, there is few research related to the inelastic buckling behavior of HRB600 steel bars or the low cycle fatigue damage model considering buckling. Focused on the undisturbed specimens of HRB600 high-strength steel bars, ten monotonic compression buckling tests and 16 tension and compression cyclic loading tests considering buckling were conducted. The average stress-strain curves and mid-span transverse displacements of buckled specimens were measured. The influence of inelastic buckling on the compressive strength deterioration of the HRB600 steel bars, and the influence of buckling direction on the strength deterioration and fatigue damage of the steel bars were analyzed. A modified low-cycle fatigue damage model suitable for HRB600 high-strength steel bars was proposed, which can consider the effect of buckling and different loading methods. The results show that the buckling direction of the HRB600 steel bars is stable under monotonic compression, and the strength deterioration is faster for larger slenderness ratios. The buckling direction of the HRB600 steel bar is unstable under cyclic loading, making the local plastic strain concentration and fatigue damage have less adverse effects on the post-buckling strength deterioration of the bars. The traditional low cycle fatigue damage model obviously underestimates the fatigue damage of buckled HRB600 steel bars, while the influence of buckling on the fatigue damage and fracture of HRB600 steel bars can be reasonably considered by the modified low-cycle fatigue damage model.