The graph of operator in closed-loop system and the robust stability margin are defined in the frame of the coprime factorization,and the sufficient and necessary conditions for feedback system are given by the graph of the plant and the inverse graph of the controller.A new multi-linear model approach is used to control a strongly nonlinear system,and reasonable operation points for nonlinear system are selected to design the corresponding optimal robust compensator with the largest generalized stability margin.Then the global robust controller is built from a weighted combination of local controllers whose outputs are weighted by the functions of generalized robust margin.The designed control system has good performance and robust stability for nonlinear system.