The coupling connection between the transmitter end of the flexible DC system and the synchronous generator can realize the efficient transfer of transient energy and improve the transient stability of the system. A complex power grid model with multiple heterogeneous power sources is established, and a coordinated control topology and strategy to improve the transient stability of complex systems under small disturbances are proposed. In order to transfer more transient energy from the synchronous generator, a new virtual coupling shaft is introduced into the system, and in order to ensure the stability of the DC system, a virtual DC generator is introduced into the DC system, and the influence of the coupling between the synchronous generator and the flexible DC system on the transient stability of the system is analyzed. The simulation results show that the proposed control strategy can significantly improve the transient stability of the system.