The invention relates to a straight key for a heat sleeve iron core support ring. A fixation base (1) and a pressure plate (2) are positioned and fixed through positioning pins (4), nuts (9) on the pressure plate (2) are used for adjusting strokes of expansion fastening blocks (3), the nuts (9) and screws (5) are in threaded connection, the expansion fastening blocks (3) are in contact with the fixation base (1) and the pressure plate (2) through an inclined surface, the expansion fastening blocks (3) are symmetrically distributed at the two sides of the pressure plate (2), the two ends of each tension spring (6) are respectively connected with the expansion fastening blocks (3) at the two sides, and the expansion fastening blocks (3) at the two sides are strained through the tension springs (6). The straight key has the following advantages: mounting and dismounting are facilitated, operation steps are simplified, and an excircle surface of a stator iron core (7) is prevented from scratches due to use of a clamp.