Flexible DC traction power systems (FDCTPSs) incorporating voltage-source converters (VSCs) brings energy recovery and power quality improvement to urban rail transit, but it requires fast and precise VSC control to deal with the abrupt load changes. This paper presents an innovative converter control strategy by integrating Linear Active Disturbance Rejection Control (LADRC) with active current feedforward mechanism. The proposed method first establishes a simplified VSC dynamic model by neglecting inner current loop dynamics. It designs a control architecture integrating LADRC to compensate for total disturbances and an active current feedforward path to mitigate known load current impacts. Parameter tuning is realized via bandwidth assignment for the linear extended state observer (LESO) and control loop. Frequency-domain analysis shows the method eliminates static errors. Pole-zero analysis reveals enhanced system stability and faster dynamics compared to PI control. Time-domain simulations in PSCAD/EMTDC validate over 80% reduction in static voltage errors and 7 times faster step response without overshoot under load variations. The study concludes that the proposed control effectively balances high-performance voltage regulation and robustness, providing a practical strategy for FDCTPSs to handle complex urban rail load dynamics.