Abstract: This paper invests the influence of the control parameters about superimposed under-excitation limiter (UEL), used in a brushless high initial response (HIR) excitation system. A single-machine infinite-bus model is derived by using the synchronous machine model with the brushless (HIR) excitation system model (IEEE Type AC2C) and a superimposed multi-segment UEL. Based on the linearized model, the relation between the auxiliary damping torque (∆MD2) provided by UEL and the pertinent parameters of UEL is extracted. With the damping torque analysis (DTA) technique, it is shown that the dynamic stability of the system can be affected by the value of the proportional gain (KP) and the internal gain (KI) of UEL. Then the time-domain simulations verify the conclusions of theoretical analysis.