Under different confining pressure,triaxial compressive strength of Maokou limestone is tested by MTS 815 test system.By calculating data,the fracture strain figure is painted and crack initiation stress and crack failure stress are obtained,it shows that: with the increase of confining pressure,three stress thresholds increase,the period of unstable crack growth is longer than uniaxial compressive strength,crack propagation is limited under confining pressure.Under the same confining pressure,circ strain is larger than axial strain,circ strain grows quickly when axial force over crack initiation stress,a sharp increase in circ strain when axial force over crack failure stress,the circ-axial stress strain curve can reflect three stress thresholds.