Abstract: We propose a new parameter tuning method for practical engineering applications to address the challenge of parameter tuning for unstable time-delay systems using active disturbance rejection control technology. First, we introduce a plant reconstruction-based approach that provides a new interpretation of the parameters of the active disturbance rejection controller, enhancing the flexibility of parameter tuning in active disturbance rejection control. Second, we establish a quantitative parameter tuning criterion to determine the maximum tolerable delay. Finally, simulation experiments demonstrate that the deviation between the delay upper bound obtained using the proposed parameter tuning method and the maximum delay upper limit achievable by the controller is within 5%. Compared with PID control and internal model control based on Pade approximation, the proposed method exhibits superior control performance.