The penetration of an edge-localized mode (ELM) into an internal transport barrier (ITB) plasma has been studied on the EAST tokamak with a flat central safety factor profile q(0) ∼ 1 recently. The experiment indicates that when the ELM inward penetration radius reaches the ITB foot region, a significant influence on the ITB plasma is manifested, leading to the shrinking or collapse of the ITB on the EAST tokamak. Observations suggest that the onset of large ELM penetration, which extremely reduces the pedestal temperature and density, can trigger the collapse of the ITB, by means of the off-axis sawtooth on the EAST tokamak. The off-axis sawtooth events contribute to a further decrement in the core stored energy after a larger ELM crash in the pedestal region. The reversal surface of the off-axis sawtooth is situated around the ITB foot. The delay time between the ELM penetration reached to the ITB foot and the followed off-axis sawtooth collapse is about 2–3 ms. It is also found that the expanding of ITB is related to the net heating power. Mechanism of ITB collapse from ELM penetration to the off-axis sawtooth triggered is not yet clear. Experimental results for understanding ELM penetration in ITB plasmas are summarized and discussed.