In multi-terminal hybrid UHVDC transmission system, one task of the DC voltage station is to maintain the DC voltage of the head-end rectifier station at its set value. Line drop must be taken into account if the head-end rectifier station is not the DC voltage station and in such a case the traditional voltage margin control method and droop control method fail to achieve static error free control of the power and voltage. Based on the idea of a master-slave control method, this paper proposes a steady-state voltage control method for a multi-terminal hybrid UHVDC transmission system. First, the voltage drop between the DC voltage station and the head rectifier station is calculated based on system topology, line resistance and current. Then the control reference of the DC voltage station is modified to achieve precise voltage control of the head-end rectifier station. In addition, an adaptive method is proposed for the case where the line resistance is changing or totally unknown. Finally, a simulation model of three-terminal DC system using the real time digital simulator (RTDS) is built and simulation results demonstrate the correctness and validity of the proposed method. This work is supported by the National Key Research and Development Program of China (No. 2016YFB0900602).