The invention relates to a detachable mechanical locking device for a gear-rack lifting system. The device comprises a mounting frame and gear locking blocks; the gear locking blocks are mounted in the mounting frame; when one gear locking block locks the rotation of a locked gear, the gear locking block and the locked gear are in line contact by a wedged surface therebetween; and the gear locking block enables the locked gear to be in a pre-tightening state or finely move through the wedged surface to realize transfer or distribution of loads among different lifting units. The gear locking blocks are pressed for fixing or released for unloading through a holding-down bolt at the upper end of the mounting frame, so that the gear locking blocks are convenient to take out; and after the position of the locked gear is changed, the contact position between one gear locking block and the locked gear is adjusted by a position adjusting structure to guarantee line contact. After the locking device works, such parts as a motor, a gear box and a gear box output gear can be totally unloaded, so that the service life is greatly prolonged, and the disassembly, the maintenance and the replacement can be performed at any time as needed. The novel locking device is higher in safety compared with traditional brake locking.