The utility model relates to a printing device of a water-based offset machine, which belongs to the technical fields of printing machines, wherein an ink transfer roll is arranged in a box body, and the ink distributor roller is connected with an ink delivery roll, ink is transferred to a forme roll through the mutually operation between the two rolls, the ink delivery roll is connect3ed with the forme roll, the lower portion of the forme roll is provided with a roller platen, and a transducer is arranged between the forme roll and the roller platen which can lead the roller platen to finish printing and tripping with the forme roll. The lower portion of the roller platen is provided with a sheet guide roll and a storage complement roll, and the forme roll, the sheet guide roll and the storage complement roll are mutually connected by an apron band, and transportation of paper block is finished by the apron band. The utility model has simple structure, convenient operation, energy saving, environment protection, high automation level, and low cost, and rubber collecting printing integrates with watermark. The same forme roll can be adopted to print fomes with different sizes, and the imprinting after being printed is clear, the paper block is not easy to be damaged. The printing efficiency can be greatly improved when the utility model is allocated on assembly lines.