The invention relates to a Y-Tb-RE alloy bar for a nuclear reactor and a preparation method of the Y-Tb-RE alloy bar, and belongs to the technical field of processing and preparing of metal materials for nuclear reactors. An alloy designed in the Y-Tb-RE alloy bar includes 49%-90% of Y, 10%-51% of Tb and the balance rare earth elements RE except for Y and Tb. After burdening is carried out according to designed compositions, smelting and homogenizing treatment is carried out under vacuum atmosphere protection, hot extrusion and drawing treatment is carried out under the approximate isothermality and atmosphere protection conditions, and a finished product with uniform element distribution and the controllable Tb linear density is obtained. According to the finished product, the room-temperature tensile strength is larger than or equal to 180 MPa, the percentage elongation after fracture is not lower than 10%, the size can be accurately 0.05 mm or below, and density deviation does not exceed 0.1 g/cm<3>; according to Tb in the finished product, the linear density ranges from 0.1 g/cm to 0.5 g/cm, and linear density deviation does not exceed 0.01 g/cm; and the Y-Tb-RE alloy bar can be used as an absorber material for a gray control bar.