The invention provides an automatic sewing device, which belongs to the field of mechanical technology. The device solves the problems of the prior sewing machines of brackets stopping cloth during sewing, complex structure and single function of sewing unit, etc. The automatic sewing device comprises an upper mechanism for sewing, a lower structure matched with the upper structure, a cutting knife assembly and a bracket to support the upper structure and the lower structure; both the upper structure and the lower structure are independent units; moreover, the upper casing and the lower casing are respectively arranged with at least one upper fixing surface and one lower fixing surface to fix on the bracket; the upper casing of the upper structure is positioned with a groove-shaped breach, so that a thread take-up rod can be put through; all the three independent units of the upper structure, the lower structure and the bracket are combined into one integral body, or a unit integratedstructure. The automatic sewing unit can fulfill different functions through combination with suitable parts and accessories according to types of cloth and stitches or demands.