A machining tool for a square bottom plastic packaging bag comprises longitudinal edges and cross edges which form into a trapezoid; an included angle d between a vertical inclined edge (3) and a lower cross edge (5) is 85 degrees; an included angle c between the vertical inclined edge (3) and an upper inclined edge (3) is 100 degrees; an included angle a between a long straight edge (1) and a lower cross edge is 90 degrees; an included angle b between the long straight edge (1) and the upper inclined edge (2) is 85 degrees. A manufactured plastic packaging bag has the advantages of satisfying packaging requirements of formed flue-cured tobacco bundles due to being in a cube shape; being high in intensity and not easy to tear or break due to the fact that the bag bottom and the bag walls are machined by an integral plastic sleeve; being high in machining efficiency and saving raw materials for machining the bag.