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In HL-3 H-mode plasma discharges, two new MHD instabilities have observed and identified. Both instabilities are localized in the outer region or the pedestal region of the plasma. The first is a low-frequency instability with f=0–50 kHz, exhibiting rapid frequency chirping and a toroidal mode number of n=3. It propagates in the ion diamagnetic drift direction, displays energetic-particle mode (EPM) behavior, and triggers continuous I-phase oscillations. The second is a high-frequency instability with f=100–500 kHz. The most unstable mode has a toroidal mode number of n=0. This instability family sometimes manifests as three frequency bands exhibiting an integer harmonic relationship. The most unstable mode frequently couples with an n=1 BAE mode in the outer region to generate numerous sideband modes. These instabilities tend to appear during the ELM-free phase and preceding ELMs, but can also be observed in Ohmic heating plasma, albeit with weaker amplitude. This most unstable mode exhibits global Alfvén eigenmode (GAE) characteristics.