The invention provides an automatic welding machine for a medical drainage bag body. The automatic welding machine comprises a film feeding frame mechanism, a welding mechanism and a traction mechanism, wherein the film feeding frame mechanism and the traction mechanism are positioned on two sides of the welding mechanism and are connected with the welding mechanism; the film feeding frame mechanism comprises a film feeding side plate, a film feeding correction assembly and a film feeding conveying assembly; the film feeding conveying assembly is assembled on a film feeding side plate of the frame; the film feeding correction assembly which is matched with the film feeding conveying assembly is arranged on the other side of the film feeding side plate; and one end of the assembled film feeding conveying assembly is connected with the welding mechanism. All actions in the scheme are automatically finished by a machine without manual work, and all shearing actions of the traction mechanism and all actions of the welding mechanism are performed simultaneously; moreover, the total time of finishing the lifting and shearing actions is shorter than the time of finishing all actions of the welding mechanism, and the working efficiency and the finished product quality are greatly improved.