The invention relates to a thread-concealed type lock rod adjusting device, which comprises a lock rod, a limit structure and a lock fork or lock. The lock fork or lock is provided with a sleeve hole which comprises an inner thread hole, one end of the lock rod is provided with an outer thread head, the lock rod comprises a rod part with outer diameter smaller than the bottom diameter of the outer thread head, the lock rod can be assembled with the lock fork or lock since the outer thread head meshes with the inner thread hole of the sleeve hole, and can move axially in the same due to the fact that the outer thread head rotates in the inner thread hole of the sleeve hole, so that the length of the lock rod in the lock fork or lock can be adjusted. As the outer thread head of the end of the lock rod is retained by the limit structure, the outer thread head of the end of the lock rod can be always completely limited in the sleeve hole of the lock fork or lock. The thread-concealed typelock adjusting device is applied to the sleeve hole with two ends open and the lock fork or lock with one end open, the lock rod can be a solid steel rod or a hollow steel pipe, the lock rod cannot be separated from the lock fork or lock, and convenience in assembling, operation and use is realized.