Soft open point (SOP) is a new type of power electronic device for power flow regulation in distribution networks. With increasing distributed generation (DG) penetration, a stable but flexible power regulation ability of SOP is particularly important. However, superposition of disturbances and uncertain factors may reduce control performance. Therefore, to enhance anti-disturbance ability and dynamic performance of SOP and improve robustness to internal uncertainties, a control strategy based on improved linear active disturbance rejection control (LADRC) of DC voltage outer loop and fast terminal sliding mode (FTSM) control of inner loop is proposed. Among them, the estimation error and the known part of the total disturbance are added to a linear extended state observer (LESO), and an improved LADRC method is proposed and applied to constant DC voltage outer loop. Then, by combining dynamic characteristic equation of AC current of SOP, FTSM surface and exponential approach equation, FTSM is applied to inner loop of the SOP to improve response speed and robustness of system. Finally, a simulation model of a three-port SOP connected to a distribution network is built, and effectiveness of the proposed method is verified.