  By analyzing large quantities of discharges in the unfavorable ion $ \vec
B\times \nabla B $ drift direction, the I-mode operation has been confirmed in
EAST tokamak. During the L-mode to I-mode transition, the energy confinement
has a prominent improvement by the formation of a high-temperature edge
pedestal, while the particle confinement remains almost identical to that in
the L-mode. Similar with the I-mode observation on other devices, the $ E_r $
profiles obtained by the eight-channel Doppler backscattering system
(DBS8)\cite{J.Q.Hu} show a deeper edge $ E_r $ well in the I-mode than that in
the L-mode. And a weak coherent mode (WCM) with the frequency range of 40-150
kHz is observed at the edge plasma with the radial extend of about 2-3 cm. WCM
could be observed in both density fluctuation and radial electric field
fluctuation, and the bicoherence analyses showed significant couplings between
WCM and high frequency turbulence, implying that the $ E_r $ fluctuation and
the caused flow shear from WCM should play an important role during I-mode. In
addition, a low-frequency oscillation with a frequency range of 5-10 kHz is
always accompanied with WCM, where GAM intensity is decreased or disappeared.
Many evidences show that the a low-frequency oscillation may be a novel kind of
limited cycle oscillation but further investigations are needed to explain the
new properties such as the harmonics and obvious magnetical perturbations.
