Abstract: To evaluate the overpressure effects of aluminum-containing explosive AFX-757 in tunnels, explosion tests were conducted using domestic GuHL-2 explosive in both semi-infinite space and long straight tunnel. Overpressure waveform curves were recorded at varying distances from the detonation epicenter, characterizing their propagation law in semi-infinite space and tunnel. A critical conversion relationship between open-space and tunnel overpressures for the explosive was established. Experimental results revealed that the shock waves in tunnel exhibited three distinct characteristics during the stable propagation phase: significantly slower decay of peak overpressure, extended positive pressure duration, and consistent impulse values. According to the experimental data of the explosion in the tunnel proposed formulations for peak overpressure and positive pressure duration in open-ended tunnel, combined with the energy concentration factor to correct the scaled distance, the ground overpressure propagation law in semi-space, and the free-field overpressure propagation law in infinite air based on the ground overpressure introduced, deduced the prediction formula for the peak overpressure attenuation of the shock waves in the tunnel. The maximum deviations of the two methods from the experimental results for the stable propagation phase of the shock waves in the tunnel were calculated to be −10.36% and 13.99%, respectively, thereby demostrating the feasibility of utilizing near-ground explosion experiments for tunnel overpressure assessment.