[Objective] To address the application requirements of unidirectional wireless power transfer (WPT) systems—including simplified receiver-side structure, cost-effective implementation, reliable operation, and fast load-side voltage stabilization—this study targets the decline in output stability of LCC-S WPT systems under coil misalignment, load variations, and rectifier-side input disturbances. A particle swarm optimization-based linear active disturbance rejection control (PSO-LADRC) strategy is proposed to enhance dynamic and anti-disturbance performance. [Methods] Based on the transmission characteristics of the LCC-S WPT system, a small-signal model of the secondary-side Buck converter was established. A secondary-side closed-loop controller comprising a linear extended state observer and a linear state error feedback law was constructed to realize the online estimation and compensation of the total disturbance. Furthermore, a multi-performance index objective function was formulated, and PSO was employed to optimize the key parameters of LADRC, thereby enhancing the overall control performance of the system. [Results] Experiments indicated that the output voltage was stabilized around 20 V under coil misalignments of 0, 2 cm, and 5 cm. When the reference voltage was stepped from 20 V to 15 V, the settling time of PSO-LADRC was 2 ms, which was only one-third of that of conventional LADRC. During the load step change from 15 Ω to 30 Ω, the settling time was reduced from 1.0 ms to 0.8 ms, and the overshoot was decreased from 2.2% to 1.9%. [Conclusion] The proposed PSO-LADRC strategy in this paper effectively addresses the issues of output voltage fluctuation and poor robustness in the secondary-side Buck converter of the LCC-S WPT system, providing technical support for the engineering application of high-performance WPT systems.