The invention relates to the technical field of building engineering, in particular to a scaffold externally hung protection device. A scaffold comprises vertical rods and transverse rods; the vertical rods and the transverse rods are connected; the periphery of each vertical rod is connected with a round disc; a plurality of connecting holes are formed in the round disc in a surrounding way; theprotection device comprises a protection screen, first connecting seats and second connecting seats; each first connecting seat is detachably connected between the round disc and the protection screen; and each second connecting seat is detachably connected between the transverse rods and the protection screen. The protection screen replaces a flexible protection net for protection; the reductionof the safety of the protection screen caused by damage occurring in the use process is avoided; through the first connecting seats, the protection screen and the vertical rods are fast connected; through the second connecting seats, the protection screen and the transverse rods are fast connected; the dismounting and the mounting are convenient; simplicity and high speed are realized; the dismounted protection screen, the dismounted first connecting seats and the dismounted second connecting seats can be repeatedly used; the generation of construction wastes is avoided; and safety, reliability and green and environment-friendly effects are achieved.