The invention discloses an automatic locking mechanism applied to a nursing bed. The automatic locking mechanism comprises a locking block, a toothed plug pin, a steering engine mounting plate, a steering engine and a gear, wherein the steering engine mounting plate and the locking block are fixed on an equipment main body; the gear and the steering engine are mounted on the steering engine mounting plate; the steering engine drives the gear to rotate by a certain angle so as to drive the toothed plug pin to move in the horizontal direction in the locking block to lock a to-be-locked shaft part, and locking motion is realized. The automatic locking mechanism is low in manufacturing cost and convenient to use and can adapt to various different situations, the trouble of manual locking is omitted, safe locking is guaranteed, and the automatic locking mechanism has the characteristics of being high in transmission efficiency, steady in transmission, compact, simple to manufacture, accurate to position, safe, stable and the like.