Abstract: The solid and gaseous residues of coal dust explosion are the physical evidence for analyzing the detonation site and propagation path and the basis for deploying rescue work. The 20 L spherical explosion system is used to conduct explosion experiments on lignite coal dust with different concentrations and particle sizes. And the particle size change of the solid residue and the flammability of the gaseous residue of the lignite coal dust explosion are analyzed. The results show that the particle size range of lignite coal dust explosion solid residues is larger than that of the original lignite coal dust. When the coal dust concentration is constant, as the particle size decreases, the D10 change rate of lignite coal dust explosion solid residues tends to increase negatively, the D50 change rate fluctuates in the range of 10% to 20%, and the D90 change rate tends to increase positively. When the coal dust particle size is constant, as the coal dust concentration increases, the D10 of the lignite coal dust explosion solid residue first decreases and then increases, while the D50 and D90 continue to increase. The lignite coal dust explosion gaseous residue mainly contains O2, CO, H2,CO2,CH4,C2H6,C2H4,C2H2 and C3H6. As the particle size of coal dust decreases or the concentration increases, the content of O2 and CO2 in the gaseous residue decreases continuously, and the content of hydrocarbon gases such as CO, H2 and CH4 increases continuously. When the coal dust particle size is constant, the flammability index of lignite coal dust explosion gaseous residue within the concentration range of 100-200 g/m3 is less than 1, indicating that the gaseous residue is not combustible. The flammability index of lignite coal dust explosion gaseous residue within the concentration range of 300-600 g/m3 is greater than 1, indicating that the gaseous residue is combustible. When the coal dust concentration is constant, the flammability index of lignite coal dust explosion gaseous residue with the particle size of 180-250 μm is less than 1, indicating that the gaseous residue is not combustible. The flammability index of lignite coal dust explosion gaseous residue with the particle size of 38-180 μm is greater than 1, indicating that the gaseous residue is combustible. The content of H2 and CO in the gaseous residue is the key factor affecting the flammability of lignite coal dust explosion gaseous residue. The flammability is mostly affected by H2, followed by CO.