Abstract: High inherent moisture,lots of oxygen-containing functional groups and poor grindability of low-rank coal lead to lower coal water slurry（CWS） concentration,which limit the subsequent gasification.To resolve these problems,taking Inner Mongolia NO.1 and NO.2 coal as research objects,compare the characteristics of two kinds of coal water slurry which are prepared by traditional CWS preparation method and preliminary grinding method respectively.The results show that,the latter method can dramatically improve the content of-0.075 mm size fraction.Stabilize the apparent viscosity at 1200 mPa.s,when the mass ratio of middings and fines is 70 to 30,the highest CWS concentration of these two coals is 61.39 percent and 58.52 percent respectively,improved by 3.92 percent and 3.94 percent respectively compared with traditional CWS preparation method.The improvement of CWS concentration is beneficial for the subsequent gasification.