The invention provides an on-line painting device, which relates to the field of cigarette package machinery. The on-line painting device, for painting coating liquid on a paper-based surface of inner backing paper, comprises a transmission mechanism for transmitting the inner backing paper, a painting mechanism for painting the paper-based surface of the inner backing paper with the coating liquid on line, a stocker for storing the coating liquid, and a driving mechanism for driving the coating mechanism to rotate automatically. The coating mechanism includes a coating roll able to rotate automatically. A coating part of the coating roll communicates with the stocker and an outer surface of the coating part of the coating roll is close to the paper-based surface of the inner backing paper. According to the invention, it can be ensured that the inner backing paper can be protected from being broken during painting process and that perfuming painting on the inner backing paper can be reliably and effectively carried out on line.