Abstract: To address the issues of poor dynamic performance and weak disturbance rejection capability in LLC resonant converters under traditional control methods, a fractional linear order active disturbance rejection controller (FOLADRC) was designed and applied to the closed-loop control system of a half-bridge LLC resonant converter. Initially, the small-signal model of the LLC resonant converter was obtained through the extended describing function method, and the system transfer function was obtained through reduction in Matlab. Subsequently,the linear active disturbance rejection control (LADRC) framework was modified by eliminating the phase-lag-inducing tracking differentiator to mitigate dynamic response delays. Concurrently, the error feedback control law in LADRC was replaced with a PD^μ controller, where the fractional-order differential term μ from the fractional-order PID (FOPID) controller was introduced to optimize system dynamic performance. This modification enabled the FOLADRC to simultaneously maintain the disturbance rejection capability of conventional LADRC and achieve the enhanced dynamic performance characteristic of FOPID control. The transfer function of FOLADRC was further derived, followed by the generation of closed-loop system Bode diagrams using Matlab to validate the controller's stability margin through frequency-domain analysis. Subsequently, a 300 W-rated experimental prototype was constructed where comparative tests were conducted employing PID, LADRC and FOLADRC control strategies. The results show that in the positive and negative load step response conditions, compared with the PID controller, FOLADRC shortens the transient adjustment time by 47.37% and 60% respectively. Compared with the LADRC, the transient adjustment time is shortened by 20% and 31.03% respectively, significantly improving the system’s dynamic response speed and anti-interference capability. This study provides an effective solution for optimizing the performance of LLC resonant converters through the integration of fractional-order control and active disturbance rejection theory.