The embodiment of the invention discloses a flexible automatic forming machine for a flat-bottom doypack. The flexible automatic forming machine comprises a rotating mould, a bagging device, a bottom pressing device and a bottom folding device. The rotating mould comprises multiple mould bodies circumferentially arranged in the radial direction at equal intervals. The bagging device comprises a pair of suction cups and a pair of prop-open mechanisms arranged at the front ends of the pair of suction cups. The pair of suction cups are installed on double-piston-rod cylinders correspondingly. The prop-open mechanisms comprise a pair of supporting plates installed on the cylinders correspondingly. The supporting plates face the pair of suction cups. The supporting plates of the pair of supporting mechanisms are used for propping open a bag opening sucked and opened by the pair of suction cups and are used for making the mould bodies sleeved with the flat-bottom doypack. The bottom folding device is used for folding and forming the bottom of the flat-bottom doypack. Due to the adoption of the flexible automatic forming machine, manual operation can be replaced, all processes of folding of the flat-bottom doypack are automatically completed, the production efficiency is easily improved, the labor input is reduced, the production cost is reduced, the folding effect of the produced flat-bottom doypack is uniform and standard, and the production quality is ensured.