Abstract: For the purpose of effective diagnosis of a class of nonlinear system with the time-varying failure of the actuator, a method of the fault accommodation was proposed based on time-varying gain extended state observer (ESO) for the inverse system. Firstly, the traditional constant gain ESO was improved by using a time-varying gain design method, which guaranteed that the "peaking value" problem in the initial phase of the state and fault estimation was effectively eliminated. Secondly, the nonlinear system was linearized to the corresponding linear system based on the compensation and regulation of the fault estimation value for the original system and the introduction of the inverse system. At this time, the system not only possessed fault-tolerant ability, but also possessed the pseudo linear characteristic whether failures occurred or not. And then, the robust guaranteed cost control was designed. The system possessed good performance as well as the robustness to the inverse modeling errors by using the same controller. Finally, a simulation example shows the effectiveness of the proposed approach.