A bag forming device, comprising at least two bag forming units, each bag forming unit being provided for passing through of a packaging film strap, wherein each bag forming unit comprises a deflection element and a folding element, the folding element comprises a forming tube, and the forming tubes of the bag forming units are arranged in a first direction in sequence, characterized in that the deflection element, the folding element and the forming tube in the folding element comprised in a same bag forming unit are configured such that: for the deflection element, the packaging film is moved from rear of the deflection element to front of the deflection element, consistent with a second direction and when the packaging film is moved around the deflection element, the packaging film moves along the following moving route: from front of the deflection element, to one side end of the deflection element, to the other side end of the deflection element that is close to the forming tube, and then moves downward parallel and opposite to a height direction of the deflection element, wherein said two side ends are left side end and right side end of the deflection element and are distributed in width direction of the deflection element, the width direction of the deflection element is in consistence with the first direction, and film moving positions are provided in the deflection element in the moving route for passing through of the packaging film to make deflection of the packaging film; for the folding element, when the packaging film is moving through the folding element, the packaging film is folded longitudinally, and longitudinal openings of the packaging films after longitudinal folding all face towards the first direction, and the packaging film moves along an axial direction of the forming tube when the packaging film is moving through the forming tube wherein the height direction of the deflection element is perpendicular to the first direction, and the second direction is perpendicular to both the first direction and the height direction of the deflection element. for the deflection element, the packaging film is moved from rear of the deflection element to front of the deflection element, consistent with a second direction and when the packaging film is moved around the deflection element, the packaging film moves along the following moving route: from front of the deflection element, to one side end of the deflection element, to the other side end of the deflection element that is close to the forming tube, and then moves downward parallel and opposite to a height direction of the deflection element, wherein said two side ends are left side end and right side end of the deflection element and are distributed in width direction of the deflection element, the width direction of the deflection element is in consistence with the first direction, and film moving positions are provided in the deflection element in the moving route for passing through of the packaging film to make deflection of the packaging film; for the folding element, when the packaging film is moving through the folding element, the packaging film is folded longitudinally, and longitudinal openings of the packaging films after longitudinal folding all face towards the first direction, and the packaging film moves along an axial direction of the forming tube when the packaging film is moving through the forming tube