Firstly, the control technology of seamless switching was studied for the microgrid system under islanded & grid-connected operation mode, which used master-slave control mode and energy storage system converter as the gird-forming unit. Then the P/Q and V/f normalized control model of energy storage converter was proposed with ‘outer parallel, inner shared’ strategy. Meanwhile, the parameter design of normalized controller was completed, as well as the stability analysis. The real-time simulation model of microgrid under islanded & grid-connected operation mode was built in the RT_Lab real time simulation platform, and the analysis of the control strategy was carried out. Finally, the microgrid seamless switching experiment under islanded & grid-connected operation mode was carried out in the National Wind Power Grid Integration R&D （Testing） Center microgrid platform, and the experiment results verified the effectiveness of the control method.