To reveal the inhibition effect of sodium bicarbonate with different particle size distributions (PSDs) on premixed methane/air explosions, four kinds of powder suppressants with different surface mean diameters D-3,D-2 (41.8-55.1 mu m) but a similar median diameter D-50 (58.6 +/- 0.7 mu m) and volume mean diameter D-4(,3) (61.7 +/- 0.8 mu m) were selected. The experimental results show that the inhibition effect varied remarkably with the PSD of powder suppressant. The ignition induction period for the methane/air mixture showed an increasing trend with the increase in the mass fraction of finer particles in suppressants. The flame front became blurred and discontinuous with the increase in mass concentration of powder suppressants. The drop rates in the peak overpressure were within 33.47 +/- 6.24-82.75 +/- 2.98%, depending on the PSD and mass concentration. The effect of PSD on the explosion suppression was more pronounced at the lower mass concentration. However, the mass concentration became the main factor affecting the suppression efficiency at the higher mass concentration. Additionally, though the D-3,D-2 was a more appropriate choice than D-50 or D-4,D-3 was, a sole variable for the powder characterization is insufficient to evaluate the suppression efficiency. The PSD, especially the mass fraction of the small particles below 31.1 mu m, should also be taken into account. More realistically, the mass of powder might be decreased as long as a reasonable PSD of the powder is employed in terms of practical applications. (C) 2019 Elsevier B.V. All rights reserved.