In this paper, the precise reflection coefficients of PP wave in EDA medium are first derived from the christoffel equation and boundary conditions. Based on this, an isotropic medium is used as the background medium to derive approximate reflection coefficient of PP wave in extremely weakly anisotropic medium. The approximate reflection coefficient of PP wave in HTI and EDA medium is derived by substituting the elastic coefficient of HTI and EDA medium into the reflection coefficient formula of PP wave in extreme anisotropic medium, and the calculation of the approximate reflection coefficient of PP in HTI and EDA media is studied through model calculations. The results show that the calculation accuracy of the approximate reflection coefficient formula is relatively high for HTI media under weakly anisotropic conditions, and the relative error is Within 7%; for EDA media with small anisotropy parameters (anisotropic coefficient <0.1), when the incident angle is less than 40 °, the absolute error of the approximate reflection coefficient of the PP wave is less than 10-3, and the relative error is less than 10 %, and its calculation error increases as the incident angle increases. For media with strong anisotropy (anisotropic coefficient reaches 0.2), the relative error reaches 35% when the angle of incidence reaches 60 °, but the relative error remains within 10% when the angle of incidence is less than 45 °. When the angle is relatively small, the calculation formula of approximate reflection coefficient of PP wave in EDA medium is still valid for the medium with strong anisotropy. The approximate study of the reflection coefficient can provide a basis for the survey line layout and offset setting of the seismic survey. It is beneficial to improve the inversion speed,By studying the reflection coefficient and linearizing the accurate reflection coefficient.