Decentralized optimal tracking control of large-scale nonlinear systems with respect to local performance criteria of subsystems is considered. A decoupled linear Two-Point Boundary Value (TPBV) problem sequence is constructed to approximate the nonlinear coupling large-scale TPBV problem, which is the necessary condition of the nonlinear optimal tracking control problem. We prove that the constructed linear TPBV problem sequence uniformly converges to the nonlinear TPBV problem. By iteratively solving this linear TPBV problem sequence, a decentralized linear feedback optimal tracking control law is obtained. An illustrative example shows the validity of the algorithm.