Abstract: In order to improve the density of the low rank coal water slurry abilities and the efciency of the gasifier, to reduce the coal consumption of the syngas and the oxygen consu mption and to improve the service life of the nozzles in the gasifier, three kinds of low rank coals from No.1 and No.2 of Hongshaquan Mine and Wucaiwan Mine were chosen to prepare coal water slurry by classified grinding technology, and compared with the conventional slurry preparation technique with a single grinde. The results showed that by using conventional slurry prepa ration technique with a single grinde, the concentration of three low rank coals were 55. 18%、51.93% and 55 .28%; while by using classified grinding technology, the concentration of three low rank coals were 58 32%、54. 94% and 58. 43%, we found that the coal water slurry concentration increased by three percent, so as to reduce the cost of production and improve the market co mpetitiveness of the coal chemical company.