This paper studies the optimal control with zero steady-state error problem for nonlinear large-scale systems affected by extal persistent disturbances. The nonlinear large-scale system is transformed into N nonlinear subsystems with interconnect terms. Based on the intal model principle, a disturbance compensator is constructed such that the ith subsystem with extal persistent disturbances is transformed into an augmented subsystem without disturbances. According to the sensitivity approach, the optimal tracking control law for the ith nonlinear subsystem can be obtained. The optimal tracking control law for the nonlinear large-scale systems can be obtained. A numerical simulation shows that the method is effective.