Ext rapolation operator of one2way wave field has great application in seismic migration imaging. According

to their implement , these operators can be classified into three kinds : Kirchhoff integral method , implicit definite

difference in space domain and Fourier t ransform method. They represent different operator expression methods. Dif2

ferent precisions will be got while using the operators in these methods in different t runcate order. Represent in sym2

bol in the method of derivation and accuracy analysis. Symbol of operator is the function of operator acting on sine

function. Symbol of operator is the extension of convolution operator’s Fourier t ransform. Fourier t ransform method

can be directly derived f rom symbol function’s separable approximation.