The invention relates to the technical field of bridge demolition, and discloses a bridge demolition safety protection device which comprises a supporting mechanism, the supporting mechanism comprises a supporting base and a supporting positioning block, a positioning groove is formed in the upper side of the supporting base, and an inclined supporting column is arranged at the position, located on one side of the positioning groove, of the upper side of the supporting base. The supporting and positioning block comprises a supporting and positioning block body, and a supporting clamping groove is formed in the upper side of the supporting and positioning block body. A movable clamping block can be moved by pulling a shifting plate, a supporting positioning block is embedded in a positioning groove, a plurality of second positioning blocks are embedded in a designated position, the loosening condition can be avoided, then the shifting plate is loosened, a spring recovers deformation, and the movable clamping block is driven to abut against a supporting base; a worker can conveniently and preliminarily fix the supporting positioning blocks and the supporting base, then a corresponding screw rod sequentially penetrates through one set of first positioning blocks and then is fixed to the supporting base, and the worker can conveniently conduct installation.