The characteristics of the tidal variation in gravity field are studied based on the long series tidal measurements observed with a superconducting gravimeter in Wuhan, China. The tidal parameters are determined accurately, the effect of the ocean loading and atmospheric pressure in gravity measurement are discussed. The complex eigen-period period and Q value of the FCN are evaluated based on the resonance observed in the diurnal tidal gravity, the gravity change due to the polar motion is also studied.The study of the geophysics using tidal gravity measurements is also discussed in the paper.