This paper compared and analyzed microstructures and discharge characteristics of aged oil-paper insulation in mine power transformer and ordinary power transformer in actual life cycle. By means of modern testing methods such as viscosity tester, optical microscope and scanning electron microscope (SEM), and according to phase-resolved partial discharge pattern (PRPD), polymerization degree, surface forms, micromorphology of oil-paper insulation, as well as its discharge inception voltages, discharge levels and discharge numbers, are analyzed. The results reveal that: synergistic effects of temperature, moisture and products lead to formation of oil-paper microstructure defects during aging, which in turn triggers electrical tree branches, and dispersion of insulation defects leads to "wave" characteristics in discharge phase distribution; in the process of operation, aging of mine transformer oil-paper insulation becomes more serious, its partial discharge (PD) phenomenon becomes more intense; operating environment of mining area is main reason for more serious aging of mine power transformer oil-paper insulation, meanwhile changes of microstructure defects in mine power transformer oil-paper insulation is more obvious, which is direct cause for more significant changes of its discharge characteristics; electrical power standards should be more strictly implement for monitoring of mine power transformer insulation state, and partial discharge can more effectively diagnose mine transformer insulation state.