The utility model discloses a mandrel used for an induction logging instrument, which belongs to the technical field of petroleum logging instruments. A mandrel body is made of non-magnetic silico-manganese bronze metal tubing and is a hollow tubulous spindly shaft, the outer wall of the mandrel body is provided with a glass fiber-reinforced plastic sleeve, the mandrel body and the glass fiber-reinforced plastic sleeve are spliced into a whole by compositing, and the outer wall of the glass fiber-reinforced plastic sleeve is provided with circular arc coil line passing grooves. The mandrel has the beneficial effects that the problems that through lines in a mandrel tube and passing lines outside a coil skeleton are mutually interfered, and the sharp points of the line grooves easily cut the lines are effectively solved; the glass fiber-reinforced plastic sleeve has a vibration reducing effect on a coil system arranged on the mandrel body; the coil skeleton can slide along the mandrel body for debugging; the problem that the processing is difficult due to the fact that long and thin holes inside the traditional mandrel bar stock are complex in processing technic is solved; and a copper tube wound with a glass fiber-reinforced plastic layer does not need to be sleeved outside the mandrel, and the independent non-magnetic silico-manganese bronze mandrel is used for replacing the structure of a conventional array induction instrument which can only be used by combining a mandrel with a copper tube, so that the structure of the instrument is simplified, and the manufacturing cost of the instrument is greatly reduced.