The ignition and flame propagation behavior of pulverized coal particles in an O-2/CO2 atmosphere was studied in a long quartz tube reactor. The effects of mixing ratio of fine (mean diameter 16 mu m) and coarse (mean diameter 82 mu m) coal particles and oxygen concentration on the ignition characteristics, flame front distance, and flame propagation velocity were investigated by capturing the flame ignition and propagation using a high-speed video camera. The experimental results show that the particle size distribution has a strong influence on the ignition and flame structure of coal particles. Smaller coal particles result in earlier ignition, a smoother flame front, longer flame, and faster flame propagation velocity. Mixing of smaller coal particles with larger ones shortens the ignition delay and enhances the propagation velocity of the flame front. For different coal particle size distributions, the variation of flame propagation velocity with time in general displays an "M"-shaped curve. The curve of flame propagation velocity vs time is single-peaked at 40% oxygen concentration for both coarse and fine particles with mean diameters of 82 and 16 mu m, respectively. The effect of oxygen concentration on the flame propagation becomes stronger as the percentage of fine particles increases. The effect of fine coal particles on the volatile release rate of coarse particles was analyzed by numerical simulation. The results show that increasing the ratio of fine coal particles shortens the time for volatile matter release from the coarse coal particles and increases the coarse particle temperature.