Abstract：The precision of converted wave time-distance equation directly affects the velocity analysis of converted wave and its NMO precision. Common-used converted wave time-distance equations include hyperbolic equation (single-parameter equation called in the paper),double-square-root equation (or called double-parameter equation) and high-order non-hyperbolic equation. Coming from the P-wave larger-offset equation and faced with the feature of converted wave propagation,the paper deduced converted wave three-parameter time-distance equation that can reflect the vertical inho-mogeneity of media,among which the three parameters mean P-wave velocity, S-wave velocity and vertical inhomogeneity separately. On that basis, the methods for three-parameter velocity analysis and NMO of converted wave have been formed. In order to comparison among the single-parameter e-quation, double-parameter equation and three-parameter equation, we use these three equations to make syntheses data and process the real data,the results showed the converted wave three-parameter equation is superior to the other two equations in precision.
