Abstract: First, this paper has deduced theoretically calculation formula of coupling coefficient of observational well-hole of borehole body strain, and according to Kelvin tidal theory set up the calculation model of tidal factor observation by borehole body strain. It has studied the relation between the change characteristics of tidal factors (δ) and elastic coefficient of rocks (E₃, υ₃), and indicated the nonliner relation of δ with E₃ and υ₃. The bigger E₃ and υ₃ are, the bigger δ is. When E₃5 ×10¹⁰pa, δ is influenced obviously. Conversely it is influenced weakly. And δ is compared and analysised with real observational data.