The invention discloses a rotating self-locking mechanism used for an on-board liquid crystal television screen, which comprises a first fixing component, a second fixing component, a rotating self-locking component, a motion bar and a switching place. A shaft fixedly connected with an active engaging mechanism drives the first fixing component and a display to realize rotating or locking by separation or engagement of the active engaging mechanism and a passive engaging mechanism of the rotating self-locking component; the motion bar is fixedly connected with the active engaging mechanism todrive separation or engagement of the active engaging mechanism and the passive engaging mechanism; the switching place limits the left and right displacement range of the motion bar; the motion bar drives a sliding gear to move left to make the sliding gear and a fixed gear non-contacted, and the on-board liquid crystal television screen can rotate freely; and the motion bar drives the sliding gear to move right to make the sliding gear and the fixed gear contacted, so that the on-board liquid crystal television screen is fixed. The disclosed rotating self-locking mechanism can realize free rotation of the liquid crystal television screen, can self lock on different positions, and is convenient for users to adjust angle in an automobile.