The invention discloses a support device for a boring bar which comprises a support body. The support device is characterized in that the support body is equipped with three cylindrical support columns which are in the mutual and uniform distribution of 120 degrees angle and extends outward of the outer circumference, and is positioned on the outer circumference of the reinforced rib structure, and the cylindrical support column is equipped with an adjustable device. During the boring process, the support device is assembled on the boring bar and carries out the rotating motion and the axial movement in the hole of the machined workpiece accompanying with the boring bar. The adjustable device is utilized to ensure that the outer circle of the rolling bearing and the surface of the inner hole of the machined workpiece have the slight pressure and carry out the rolling contact, and the single-support suspension boring bars of the machined workpiece with different inner diameters are supported, the defect of vibration and bending as well as deformation caused by the suspension boring bar is eliminated, and the machining requirement of promoting the boring dimension and the axial accuracy is achieved. The support device for the boring bar has the advantages of simple structure, convenient assembly, strong practicability, high standardization and generalization of parts and components, and having the certain popularization value.