Abstract: In this paper, for a voltage source converter based multi-terminal DC transmission（VSC-MTDC） system connected with offshore wind farms, a self-adaptive and hierarchical control scheme was proposed to consider the optimal allocation of imbalanced power when wind energy fluctuation occurred frequently. The equivalent extra cost function in the form of active/reactive power and voltage on the valve side was deduced firstly in details. Based on the incremental cost curve of extra generation and DC voltage at the point of common coupling（PCC）, the scheme can locally make the unbalanced power be shared economically without central controller, having similar effect to the equal increment principle（EIP）. Principles of control parameters setting was discussed based on control characteristic analysis and stability analysis. Finally, a 4-terminal radial system was used to verify the effectiveness in PSCAD/EMTDC simulation platform. The results show that the proposed scheme can reduce the extra generation cost effectively under normal conditions, and maintain DC voltage stability and power balance when the fault occurs.