<p>This paper investigated the smoke exhaustion characteristics and critical shaft height in a slope tunnel with naturally ventilated shafts based on reduced-scale tunnel experiments. The effects of longitudinal fire location, shaft setting, heat release rate (HRR) and tunnel slope on smoke exhaustion were studied. Experimental results show that the slope has great effect on smoke exhaustion. Moreover, the critical shaft height for complete smoke exhaustion of slope tunnels was studied theoretically and experimentally. The research indicates that the critical shaft height exhibits no dependency on the HRR. Notably, with the increasing of shaft length, the critical shaft height firstly decreases and then remains stable until it finally decreases to zero. Simultaneously, the critical shaft height increases with the increase of the slope and the distance between the shaft and the fire source. In addition, a theoretical model for predicting the critical shaft height was established and verified. The research results can provide some reference for the design of natural ventilation smoke exhaustion with shafts in slope tunnels.</p>