A roll control device of a vehicle curtain is mounted on a receiving housing and is connected to a curtain rod for wrapping a curtain fabric. The roll control device has a cover, a gear set mounted in the cover, and a one-way transmission assembly and a damping member respectively mounted on a first gear and a second gear of the gear set. The damping member provides rotational resistance to the first gear. When expanding the curtain fabric, with the one-way transmission assembly, the curtain fabric can be easily drawn. When retracting the curtain fabric, with the torsional resistance, the curtain fabric can be smoothly and gently wrapped on the curtain rod without causing noise and excessive vibration.