The present invention relates to an adjustable bolt electrical heating rod. The defects are overcome that a current bolt electrical heating rod has a constant length, is only suitable for heating bolts with one length specification and cannot meet the requirements of heating bolts with a plurality of length specifications. The adjustable bolt electrical heating rod comprises a front heat insulation segment, a heating segment and a back heat insulation segment which are connected in order. The back heat insulation segment is connected with a connection segment capable of position adjustment through axial movement with respect to the back heat insulation segment, the maximum external diameters of the front heat insulation segment and the connection segment are both larger than the external diameter of the heating segment, and the maximum external diameters of the front heat insulation segment and the connection segment are adaptive to the aperture of the bolt bore. The connection segment is axially moved with respect to the back heat insulation segment so that the length between the front heat insulation segment and the back heat insulation segment is changed and the apparent length of the heating segment is changed, and the length of the heating is adjusted after an electrical heating rod is inserted into a bolt bore so that the adjustable bolt electrical heating rod is able to adapt heating requirements of bolts with a plurality of length specifications.