Abstract: We analyze the gravity data observed before and after March 11,2011 when the Mw9.0 earthquake occurred in the sea areas nearby the East coast of Honshu,Japan,with the method of co-seismic response signal analysis.We also provide the observations of long-period seismic surface waves and free oscillations recorded by gPhone gravimeter after the great earthquakes.Processed by band-pass filter,the data obtained within 12 hours after the earthquake can be recognized the records of 7 Rayleigh surface waves spreading around the Earth.In the low frequency domain(5 mHz or less),43 fundamental modes and at least 52 harmonic modes of Earth's free oscillations can be detected,the distributions of which are in good agreement with the theoretical modes.Meanwhile,at the low frequencies less than 1 mHz,spectral splitting of 4 modes is observed.