Abstract: In view of the pollution caused by the large storage of coal gangue and the shortage of natural aggregate in concrete, using coal gangue as coarse aggregate is a reasonable way to solve the above problems. In order to reveal the mechanical properties of coal gangue concrete and promote the application of coal gangue concrete in the field of civil engineering, the mechanical response of coal gangue concrete under multiaxial stress state is studied. Three kinds of concrete mix ratios with coal gangue volume substitution rates of 0, 30% and 50% were designed. 225 specimens were prepared for true triaxial compression test of coal gangue concrete. A total of 20 true triaxial compressive stress ratios, including four minimum principal stress ratios (σ₁/σ₃ = 0.05, 0.08, 0.13, and 0.16) and five Lode angles (θ = 0°, 15°, 30°, 45°, and 60°) were designed in the experiments. The failure modes, strength characteristics and triaxial compression strength improvement of concrete with different coal gangue replacement rates under different stress ratios were compared and analyzed, based on the triaxial compression test results of coal gangue concrete, a multi-axial strength failure criterion considering the replacement rate of coal gangue was established. The results show that the multiaxial failure modes present four types (Cylindrical failure mode, Slice shape failure mode, Oblique shear failure mode, Extrusion fluid failure mode) with the change of stress ratio, and have little correlation with the replacement rate of coal gangue. With the increase of σ₂/σ₃, the compressive strength increases first and then decreases, and the maximum value is at θ = 30°. When σ₁/σ₃ is small, the effect of σ₂/σ₃ on the triaxial compressive strength is not obvious. The larger the σ₁/σ₃ is, the more significant the effect of σ₂/σ₃ on the triaxial compressive strength is. The higher the replacement rate of coal gangue, the lower the triaxial compressive strength, and the greater the σ₁/σ₃, the more obvious the strength decrease; when σ₁/σ₃ is small, there is little difference in the improvement degree of triaxial compressive strength between coal gangue concrete and ordinary concrete. When σ₁/σ₃ is large, the improvement degree of strength of coal gangue concrete is significantly lower than that of ordinary concrete. The established failure criterion considering the replacement rate of coal gangue is well fitted with the triaxial compression test results of concrete. It can correctly reflect the influence of coal gangue coarse aggregate on the multiaxial mechanical properties of concrete, and can be used to predict the multiaxial strength of coal gangue concrete with different coal gangue replacement rates and different stress ratios. The research results can provide data reference for the practical engineering application of coal gangue concrete, in order to realize the solid waste utilization of coal gangue.