Modular multilevel converters (MMCs) have become a mainstream solution for voltage-source-converter high-voltage direct current (VSC-HVDC) links, where station-level control must simultaneously guarantee fast power regulation and strong disturbance rejection. Conventional dq-frame dual-loop vector control based on proportional-integral (PI) regulators is effective in steady state, but it often exhibits a slow transient response and noticeable overshoot when the operating point changes or when grid-side disturbances occur. To improve dynamic performance without introducing an overly complex tuning procedure, this work develops a station-level dual-loop vector controller for MMC-HVDC based on second-order linear active disturbance rejection control (LADRC). The proposed design integrates a linear extended state observer with a bandwidth-parameterized error feedback law so that internal model uncertainties and external disturbances are lumped into a generalized disturbance and compensated online. A two-terminal MMC-HVDC electromagnetic transient model is implemented in PSCAD/EMTDC to evaluate the controller under power and DC-voltage perturbations. Compared with the PI baseline, the LADRC-based scheme reduces overshoot and shortens settling time while maintaining decoupled active and reactive power tracking.