The invention provides a waist locking device comprising a mounting bracket, a C-type bracket and a arm-folding mechanism. The waist locking device is characterized in that the mounting bracket is fixedly connected with the C-type bracket; two waist tightening mechanisms are symmetrically disposed on the inner side wall of the back of the C-type bracket; the waist tightening mechanisms are fixedlyconnected with the C-type bracket through a tightening base; the tightening base is arranged inside the C-type bracket; the arm-folding mechanism is formed by the rotating connection of an arm folding plate and the C-type bracket via an arm-folding rotation mechanism. The waist locking device has the advantages of having strong rigidity, providing good support for the waist, avoiding loosening and sloshing so as to cause danger or sprain the waist due to insufficient support of a waist locking device when using the instrument, adjusting tightness quickly and conveniently with a two-way ratchet mechanism, and being safe, reliable and not easy to cause danger due to misoperation.