A turbulent coal jet flame is employed to simulate the rapid devolatilization of pulverized coal in practical coal combustion. The variation of the size and internal structure of coal particle during devolatilization were investigated through a sampling analysis technique. It is found that the volume of coal particles obviously expands during the devolatilization and the extent of the expansion heavily depends on the particle size and heating rate. During the devolatilization，the hollow structure of coal particles is formed due to the rapid release of volatile，which can result in more rapid combustion of char particles.