Abstract：In wave equation migration using finite element method, a great deal of comput- er's internal storage and computer time are used because of too many volved. The key to successful application of this method in real data unknowns in- processing lies in appropriate spacial grids and time iteration step size. Stability theory must be used as guidance for solving this problem. There is no significant critical formula of stability in the previous literatures of the field because it is quite difficult to solve for the characteristic value of big matrix. The critical formula of stability in finite e1- ement computation schema is deduced by adopting the decomposition in which direct matrix multiplication is made.
