Abstract: Flotation process is currently the most efficient and widely used method for the treatment of fine coal.The use of the XJM series flotation cell accounts for the lion′s share among the flotation equipment applied in China, which is estimated to be over 70%.In order to enable fellow workers to gain a deeper insight into the machine, the paper presents an outline of the working principle, design concept and structural features of the machine.Following a review of the process of the R & D of the machine, an introduction is made to the criteria for directing the scale-up of parameters in design of large-size ones.The structure of the machine is verified and optimized by means of flow field numerical simulation.Furthermore, a comparison is made of the main features, field application results and performance in upgrading of low-rank coal of the nowadays commonly used XJM-S, XJM_KS and “3+2” series flotation machines.Result of field application shows while ensuring the reliability of the XJM series machine, the flotation process can be rendered more flexible through making diversified combination of cells and improvement of automatic control system.Finally, the paper looks forward to the developing trend of the XJM-S series flotation machines.