To improve the leakage performance of the turbine interstage seal， a stepped labyrinth seal structure with a diversion channel is designed. The influence of the diversion channel on the leakage and heating characteristics of the labyrinth seal is investigated under various pressure ratios and rotational speeds， and compared with the smooth labyrinth seal. The results show that adding a diversion channel on the casing enhances the sealing effect of the labyrinth seal by allowing airflow at the outlet to be rolled and sucked into the channel under the effect of centrifugal force. The larger the circumferential clearance rate β of the diverter channel， the better the sealing performance. When the circumferential clearing rate β is 3， the insulated wall flow coefficient is 13.47% and the insulated wall wind resistance temperature rises by 48.7 K. The increase in the number of diversion channels intensifies the leakage of the seal. As the pressure ratio grows， the sealing leakage increases， and the diversion channel may guide the core flow return， so the leakage growth rate gradually slows down while the insulated wall wind resistance temperature rise growth rate increases. As the rotational speed increases from 3×10³ r/min to 2.1×10⁴ r/min， the airflow friction diffusion worsens， the labyrinth seal insulated wall flow coefficient decreases， the insulated wall wind resistance temperature rises， and the diversion channel improves the labyrinth seal’s sealing effect at high rotational speed.