Featuring low communication requirements and high reliability, the voltage droop control method is widely adopted in the voltage source converter based multi-terminal direct current (VSC-MTDC) system for autonomous DC voltage regulation and power-sharing. However, the traditional voltage droop control method with fixed droop gain is criticized for over-limit DC voltage deviation in case of large power disturbances, which can threaten stable operation of the entire VSC-MTDC system. To tackle this problem, this paper proposes an adaptive reference power based voltage droop control method, which changes the reference power to compensate the power deviation for droop-controlled voltage source converters (VSCs). Besides retaining the merits of the traditional voltage droop control method, both DC voltage deviation reduction and power distribution improvement can be achieved by utilizing local information and a specific control factor in the proposed method. Basic principles and key features of the proposed method are described. Detailed analyses on the effects of the control factor on DC voltage deviation and imbalanced power-sharing are discussed, and the selection principle of the control factor is proposed. Finally, the effectiveness of the proposed method is validated by the simulations on a five-terminal VSC based high-voltage direct current (VSC-HVDC) system.