In order to study the mechanical properties of pebble concrete under tri-axial compression， the conventional tri-axial test of 27 pebble concrete specimens were carried out. The failure patterns of specimens were observed， the whole stress-strain curves and their characteristic point parameters were obtained. The influence of confining pressure on the mechanical properties of pebble concrete was deeply analyzed. The results show that with the increase of confining pressure， the failure pattern of pebble concrete specimens changes from axial splitting failure to oblique shear failure， and then to transverse shear failure. The greater the confining pressure， the greater the peak stress， peak strain and initial elastic modulus， and the smoother and plumper the whole stress-strain curve after the peak stress. The calculation formula of mechanical indexes and parametric constitutive equation of pebble concrete under tri-axial compression are proposed， and the calculated results fit well with the test results.