Abstract: Two methods were used to modify the chemical sludge. The effect of the amount of modified chemical sludge on the slurryability, rheological and combustibility properties of sludge-coal water slurry(S-CWS) was studied in order to obtain process parameters of preparing high concentration of S-CWS. The results showed that the properties of S-CWS modified by NaOH were better. The better slurryability of the S-CWS was obtained when 10%~20% modified sludge was added. Compared to the general water slurry, the combustion performance of the S-CWS with the modified sludge increased.