<p>Industrial oily sludge, a kind of hazardous waste with high calorific value, can be blended with coal to effectively and efficiently utilize its energy potential while simultaneously reducing environmental pollution. The three-peak gradation technique was used to pre-modify the surface of coal particles, and the effects of various modification methods and second liquids on the rheological properties of ultra-high concentration coal-water paste (CWP) were investigated. The second liquids utilized included industrial kerosene, aviation kerosene, silane, and oily sludge, and the contact angles and infrared spectra of the coal particles modified with different second liquids were measured. The optimal dosage amount of oily sludge when utilized as the second liquid was found to be 1.8%. By employing a laser confocal scanning microscope, it was observed that the oily sludge uniformly wrapped around the surface of the coal particles to form a hydrophobic oil film, which enhanced the surface hydrophobicity of the coal particles. Ultimately, the CWP with good fluidity and a 73% concentration was prepared. This approach demonstrates potential for the preparation of ultra-high concentration CWP with superior fluidity.</p> Graphic Abstract <p></p>