In this article, we propose a unified voltage control for grid-forming inverters, which enables to flexibly synthesize six commonly used voltage control methods through a universal and simple structure. The unified control scheme is composed by three loops, i.e., the voltage magnitude control, the virtual impedance control, and the voltage-reference-feedforward control. By flexibly combining the three loops and applying different forms of virtual impedance, the six voltage control methods can be readily realized. The experimental tests confirm the effectiveness of the unified voltage control structure.