Abstract:Approximate expression as the function of ray parameters can be derived from the accurate P-SV reflection coefficient formula. The approximate expression shows that when in non-normal incidence,P-SV reflection coefficient mainly depends on two elastic parameters:1)p/p,the ratio of bulk density difference to average bulk density from bath sides of an interface;and 2) a Jp ,the ratio of shear modulus difference to average bufk density. Numerical example result is given to show computation accuracy of the approximate expression,and compared with the numerical recults of Aki and Richards'(1980)approximate formula. The applicability of our approximate expression is analysed here. The inversion parameters computed by using damped least-squares inversion theory demonstrate that in AVO data linear inverlion,estimation is mare accurate than△.(Poisson ratio difference)estimation.