The invention discloses a spinning positioning mechanism on a screen frame flanging machine. A spinning positioning mechanism is fastened to a top plate of a portal frame through bolts. A flanging and spinning mechanism is fastened to the surface of a workbench through bolts. A through matching hole which is tightly screwed with a screw rod is machined in a handle of the spinning positioning mechanism. The two ends of the screw rod are supported by round roller bearings. A sliding groove side plate is fixed to a bottom plate through another bolt, the bottom plate is fixed to a pair of side plates of the portable frame through bolts, and the side plates are welded to the surface of the workbench. A slide block is fixed to a spinning positioning head through another bolt, and the spinning positioning head is fixed to a bracket. A rectangular guide rail is installed at the bottom of the slide block, and a rectangular guide rail groove is formed in the bottom plate. A pair of bearings and a short shaft are installed in the spinning positioning head, and the other end of the short shaft is fixed to the bracket through another nut. The included angle alpha between the installation end surface of the spinning positioning head and the cylindrical surface of a workpiece is 7-10 degrees. The oblique line of the bottom surface of a cone C of the spinning positioning head is parallel to the surface of the workbench.