Abstract: In this paper, the strength and deformation characteristics of tailing under high pressure were studied with triaxial tests on three kinds of tailing. It was found that the amount of the grains broke increased with the shear strain and confining pressure, independent of the initial density of the specimen. The shape of Mohr envelops under high pressure was somewhat curved. The internal friction angle in the range of testing confining pressure （below 70 kg/cm2） was less than that under the normal confining pressure （below 10kg/cm2） by 8° 13° which is smaller than that of sand in the same conditions. Therefore, in the analysis of the stability and deformation of high tailing dams, it is necessary to take account of this effect and to compute shear strength, tangent modulus and tangent Poisson's ratio according to the results of the experiment.In this paper, the tangent modulus and the tangent Poisson's ratio computed with internal friction angle under convenient pressure and with non-linear variability of strength under high pressure were compared. The result shows that the tangent Poisson's ratio computed with the relationship proposed by Daniel is in conformity with the testing data, but the value obtained by assuming the relationship between the axial strain and lateral strain as hyperbola differs from the testing data.