Abstract: In this paper, based on the no nlinear response of rock strain and stress, we have analized the physical mechanism of loading and unloading response ratio of the earth tides of, bulk strain, and the calculation method of loading and unloading response ratio of the earth tides of bulk strain is given. We took the observed values of the bulk strain at the Chang ping and Fenfeng stations as example, calculated the loading and unloading response ratio of the earth tides of bulk strain. Before the moderately strong earthquake the response ratio has shown the variation of increase.

Key words: Bulk strain, Earth tide, Loading and unloading response ratio