Explosion pressure and pressure rise rate are two important indicators of the severity parameters of coal dust explosion. Ignition delay time has a significant effect on the explosion severity parameters of coal dust/air mixtures. In this work, this effect was studied through a combination of experiment and numerical simulation. The 20-L spherical vessel explosion test system was used to study the severity parameters of coal dust/air mixtures at the concentration of 250 g/m(3) under different ignition delay times. The results showed that both of the maximum explosion pressure and the maximum rate of pressure rise appear a trend of first increase and then decrease with the increase of ignition delay time, reaching its maximum at 60 ms. Besides, the numerical simulation was conducted to investigate the distribution and variation of gas flow, coal dust particles, and turbulence kinetic energy before ignition in detail. The simulation results were in good agreement with the previous research data, and the effect of ignition delay time on the explosion severity parameters of coal dust/air mixtures was analyzed from the aspect of mechanism. (C) 2018 Elsevier B.V. All rights reserved.