Abstract: For deep rock mechanics and subsurface engineering, accurately characterizing and evaluating rock heterogeneity as well as analyzing the correlation between the heterogeneity and physical and mechanical properties of rocks are critical. This study investigated the characteristics of acoustic emission signals produced in the process of strong and weak phase damage to rocks. The failure mechanisms of the strong and weak phases were analyzed by performing Brazilian splitting tests on different metagabbros and granites. The strong–weak phase ratio of the rocks and the uniformity of their spatial distribution were characterized. Test results show that as the feldspar develops, the strong-phase ratio of the metagabbro increases. However, the spatial distribution of feldspar minerals in the metagabbro becomes less uniform. The mineral spatial distribution uniformity in the altered granite is good; however, its strong-phase ratio is low. Furthermore, the strong-phase ratio of the typical granite is high; however, its mineral spatial distribution uniformity is poor. Moreover, uniaxial and triaxial test results show that the peak strength and elastic modulus of the rocks are related to the strong–weak phase ratio and mineral spatial distribution uniformity of the rocks. This study provides a new analytical method for the mechanical evaluation of deep rocks.