  An extension of the Luscher's finite volume method above inelastic thresholds
is proposed. It is fulfilled by extendind the procedure recently proposed by
HAL-QCD Collaboration for a single channel system. Focusing on the asymptotic
behaviors of the Nambu-Bethe-Salpeter (NBS) wave functions (equal-time) near
spatial infinity, a coupled channel extension of effective Schrodinger equation
is constructed by introducing an energy-independent interaction kernel. Because
the NBS wave functions contain the information of T-matrix at long distance,
S-matrix can be obtained by solving the coupled channel effective Schrodinger
equation in the infinite volume.
