An apparatus for printing a beer barrel includes a workbench (1), and a hydraulic pushing device (2), a barrel outer-sided printing device (3), and a barrel inner-sided printing device (4) installed on the workbench (1). The barrel inner-sided printing device (4) has a turntable (41) rotating with respect to the Z-axis and mounted on the barrel (5), an inner mold (61) installed onto a circumferential surface of the turntable (41) for printing the inner side of the barrel (5). The barrel outer-sided printing device (3) has a connecting frame (31) moving linearly along the Y-axis direction. The connecting frame (31) has an outer mold (62) for printing an outer side of the barrel (5), and the hydraulic pushing device (2) controls the outer mold (62) to move linearly along the X-axis direction. The outer and inner molds (61, 62) print a sidewall of the barrel (5). This invention prevents unnecessary waste of manufacturing cost and time caused by the scrap of semi-finished products whose previous printing process becomes useless.