The invention discloses a heat treatment device and method for improving performance of the round steel bar saw cutting end portion, and belongs to the technical field of a round steel bar heat treatment device and method. The heat treatment device and method are used for removing the area, influenced by saw cutting, of the round steel bar end portion. A bar end portion positioning and detecting mechanism is used for conducting precise infrared positioning on the end portion of a round steel bar obtained after saw cutting, then, a plane end portion induction heating mechanism is used for conducting induction heating on the end portion of the bar, online tempering treatment is conducted on the end portion of the bar, and a moving and positioning mechanism can move the plane end portion induction heating mechanism. According to the heat treatment device and method, the phenomenon of end portion cracks or delayed cracks of a martensitic structure generated after saw cutting of the end portion of the round steel bar in later production can be effectively eliminated, the performance of the end portion of the round steel bar meets the later procedure production requirement, the bar cut loss rate is reduced, and the later procedure production rhythm is increased; and the targets that the production cost is saved, the production time is shortened, and the production efficiency is improved are achieved, and very good economic benefits and popularization value are achieved.