Abstract: Ximeng lignite was pyrolyzed at different temperatures and different characteristics including coal property, slurry ability, rheological behavior and stability of coal water slurry made from char were investigated. Pyrolysis was conducted in absence of air. Viscosities of different density slurries were measured and the curves of rheological behavior were fit through shearing rate and apparent viscosity. Actual slurry density and stability was measured according to national standard method. The mechanism of pyrolysis for raw coal and char slurry was analyzed through the alteration of surface functional groups and pore structure. The results show that pyrolysis could reduce oxygen-containing functional groups in samples and bring down their hydrophilicity, which is benefit to the improvement of slurry density. Water slurry density shows first an increase, and then decrease with the rise of temperature. Pyrolysis seems to be unfavorable to the stability of slurry. Pore structure is changed a lot through pyrolysis due to the decomposition of oxygen-containing groups. Specific surface area and pore volume first increase, and then decrease, but average pore diameter shows a totally opposite trend.