To realize system integration and optimization of a high-voltage grid and AC/DC microgrids, there has been focus on the solid-state transformer (SST). However, the coordinated control of system operation modes and the optimal power allocation of plug-and-play units under line or communication fault conditions are rarely considered. Thus an adaptive mode switching and power management strategy is proposed for an SST-based active distribution network. First, the SST-based system achieves seamless mode switching among high-voltage grid connection, microgrid interconnection and microgrid islanding, ensuring that the bus voltage is stable around the rated value. At the same time, economic balanced power allocation is realized according to the operational cost and energy storage SOC applying the distributed consensus algorithm and improved droop control. Finally, the proposed mode switching and power management strategies are tested on the RT-LAB-based real-time simulation platform. This work is supported by the National Natural Science Foundation of China (No. 52107199).