Abstract: The control theory of series DC power flow control was presented, the impacts of the DC voltage and line equivalent resistance on DC line power flow were analyzed. Based on these studies, a new DC power flow controller was proposed. Compared to existing studies, the proposed DC power flow controller which is based on dual active bridge（DAB） structure and without external power supply required, is able to control the bidirection power flow of the DC line. PSCAD/EMTDC software simulations were carried out in a two-terminal and double-line VSC-HVDC（voltage source converter based high voltage direct current） transmission system series connected with the proposed DC power flow controller. The steady state and dynamic response characteristics of the DC power flow control were studied accordingly. Furthermore, dynamic experimental verifications were also carried out using the experimental prototype of the proposed DC power flow controller. The simulation and experimental results show that the proposed DC power flow controller in this paper can effective control the DC power flow control as defined.