The coal dust is polydisperse in the coalface of longwall mining. Thus,the evaluation of the explosion risk of coal dust by single particle size is defective. In order to investigate the effect of dispersion on the characteristics of coal dust explosions and find the appropriate expressive ways of average particle size to estimate the explosion risk,five coal samples with the same particle size distribution range whereas with different dispersions were investigated. The 20 L explosion sphere vessels experimental device was used to measure four parameters of the sample,including the maxi- mum explosion pressure (Pex ),the maximum explosion pressure rise rate ((dp / dt) ex ),the period from the ignition to the maximum explosion pressure ( t1 ),and the period from the ignition to the maximum explosion pressure rise rate (t2 ). Calorific value analysis and scanning electron microscopy were used to investigate the degree of reaction of coal dust with different dispersions. The diversities between the measurement results of different groups were investigated by the analysis of variance. The correlation between various particle size representation methods and the explosion charac- teristics parameters were investigated by Spearman correlation analysis. The experimental results showed that the dis- persity had a great significant influence on the explosion reaction rate of coal dust with the same particle size span. The larger the mass fraction of small coal dust particle size is,the faster the reaction rate,the more complete the reaction and released energy. When the small particles accounted for 30% ,the (dp / dt) ex increased significantly,t1 and t2 de- creased significantly. The explosive products of the original sample 3 with small particle size had the lowest calorific value and rich pore structures on the particles surfaces,which could proved that the explosion reaction degree of the fi- ner coal dust can be increased due to the accelerating devolatilization rate. The Spearman correlation coefficients be- tween D10 ,D25(the particle size for which 10% and 25% of the particles by the projection area),D3,2( Sauter mean diameter) and (dp / dt) ex ,t1 ,t2 fall within highly-correlated and significantly-correlated intervals. It showed a good cor- relation. D10 ,D25 and D3,2 are the appropriate methods to describe the dispersion of polydisperse coal dust for investiga- ting the explosions.