Abstract: The overall capacity of compression type anchor cables is influenced by the compression capacity of the mortar in front of bearing plate. For assessing the capacity of the mortar, the compression failure process of anchoring mortar under actual stresses is simulated by a self-adaptable multiaxial stress loading device on a uniaxial test machine. The mixture ratios, proportions and holes of cylindrical mortar specimens are made according to engineering conditions. The normal and tangential stresses decided by theoretical and experimental researches are exerted on the side face of the mortar. The compressive strengths, stress-strain curves and failure patterns of mortar specimens are obtained by the tests. The results show that the compressive strengths of the mortar are enhanced by the lateral normal and tangential stresses. By comparing laboratory experiment with field test results, empirical formulas for predicting the enhancement effect and the empirical relationship of rock compressive strength and lateral stresses are suggested.