Abstract:Based on the function relationship between gravity coefficient and the Earth orientation parameters (EOP), we estimate second-degree spherical harmonic gravity changes ΔC21 and ΔS21 from 1980 to 2013. Comparison of the ΔC21 and ΔS21 provided by SLR, shows that they agree well with each other. Moreover, we find a 6-year periodicity exists in ΔC20 provided by SLR. Otherwise the amplitude is just 1/10, as compared with the 6-year signal of LOD. This indicates that the 6-year periodicity of LOD is not excited by the atmospheric and oceanic hydrologic motion and the Earth’s body, although the exact mechanisms are still not understood.