Abstract: With the help of the decline method, a computer-aided analysis program of Christoffel equation is described which makes it possible to calculate elastic constants and viscous constants of any crystals precisely and easily. The elastic constants of LiNbO₃ and Bi₂GeO₂₀ crystal are calculated with Apple-II computer with the Fortran program which we suggested before, and the calculated figures are compared with values obtained by others.