Self-positioning universal chuck

The utility model relates to a self-positioning universal chuck which is mounted on a chuck of a numerical control machine tool. The self-positioning universal chuck comprises the chuck, a main positioning block, a fixing block, a compressing block, a locking block, a guide rod, a compressing screw, a locking screw I and a nut I, wherein a main guide track groove is formed in the chuck, the nut I is arranged in the main guide track groove, the main positioning block and the fixing block are oppositely arranged on the chuck, through holes I are formed in the main positioning block and the fixing block, the locking screw I is matched with the through holes I and the nut I, a through hole II is formed in the fixing block, the guide rod is matched with the through hole II, a threaded hole I is formed in the fixing block, a through hole III is formed in the locking block, and the compressing screw is matched with the through hole III and the threaded hole I. During use, the self-positioning universal chuck only ne