The provided are a four side seal packaging bag and a preparation device and method thereof. The preparation device includes at least: a film material conveying mechanism, configured to continuously convey a film material of a packaging bag along a length direction of the film material; a folding mechanism, configured to fold the film material conveyed by the film material conveying mechanism; a cutting mechanism, configured to cut the upper film material; punch-and-cut mechanisms, configured to form square punch-and-cut regions and separate the square punch-and-cut regions from the side accordion film materials; a side accordion forming mechanism, configured to perform a forming operation on the side accordion film materials; and a hot-sealing mechanism, configured to hot-seal the upper film material, the formed side accordion film materials, and the lower film material.

A counter-pressure roller for applying pressure on a longitudinal sealing of a packaging material web comprises, a first back-panel support section having a first radius and a second back-panel support section having a second radius, for supporting first and second back-panels of the web, respectively. The first radius is greater than the second radius, and a groove is between the first and second back-panel support sections, for holding a longitudinal overlap section formed by first and second edge sections of the first and second back-panels, respectively. The first edge section is positionable outside the second edge section, with the first edge section facing a bottom of the groove. The bottom has a third radius less than or equal to the second radius. The groove has a first groove edge section having a first inclination, and a second groove edge section having a second inclination.