Background <p>Compared to gas-driven shock tubes, the explosively driven shock tubes (EDSTs) in straight form are more applicable to simulate explosive shock wave. However, there are still few studies on the propagation characteristics of shock wave and the formation distance of uniformly distributed planar shock wave (referred to as the characteristic distance in this paper) inside the EDSTs.</p> Objective <p>The study presents a method for determining the characteristic distance within the EDSTs in straight form and analyzes the differences in characteristic distance, overpressure peak, and impulse of the shock wave under typical cases.</p> Methods <p>To ascertain whether the shock wave is planar and uniform at a given distance, a novel method is proposed according to the weighted coefficient of variation (WCV, which is a dimensionless quantity used to characterize the degree of data dispersion) of the peak overpressure and impulse of the shock wave.</p> Results <p>The experimental and simulation results show that when shock wave propagates in the tube, the uniform spatial distribution of the impulse and planar spatial form on the wave front are satisfied first. Afterwards, the uniform spatial distribution of the peak overpressure on the wave front is gradually satisfied. Therefore, when the WCV of the peak overpressure tends to be consistently small, it is presumed that the shock wave has reached the characteristic distance.</p> Conclusions <p>By using the characteristic distance determination method, it was found out that the characteristic distance is mainly affected by different straight tube models, where the detonation point is located and how the explosive is shaped.</p>