NOVELTY - Treating an oily sludge comprises: adding polyacrylamide flocculating agent and polyoxyethylene ether and an oily sludge into a sludge concentration tank to perform a sedimentation separation process, separating water from the sludge and then injecting into a sewage treatment plant and then injecting into a spiral centrifuge to perform a solid-liquid separation process; hardening and tempering the oily sludge in a sludge tempering tank; heating the sludge; extracting heavy oils from the sludge; and performing a catalytic cracking of heavy oil form the sludge using a catalyst.    USE - The method is useful for treating an oily sludge (claimed).    ADVANTAGE - The method is capable of treating the oily sludge in an efficient and environmental-friendly manner, and removing organic matters from the sludge in a simple manner.    DETAILED DESCRIPTION - Treating an oily sludge comprises: injecting an oily sludge into a sludge concentration tank, adding polyacrylamide flocculating agent and polyoxyethylene ether to perform a sedimentation separation process, separating water from the sludge and then injecting into a sewage treatment plant, injecting the lower water-containing sludge into a spiral centrifuge to perform a solid-liquid separation process and then filtering using a vacuum drum filter, and separating a sludge cake from a filter cake obtained from the centrifuge; hardening and tempering the oily sludge into a sludge tempering tank with a mechanical stirring process, 0.5-1 wt.% of mass transfer strengthening additive to the sludge, and uniformly stirring the mixture, where the additive comprises a mixture of acrylic acid, N-dodecyl acrylamide and butyl acrylate copolymer and non-ionic surfactant with a mass ratio of 10:1-3, the copolymer has an atomic mass of 5000-15000 Dalton, and the molar ratio of acrylic acid, N-dodecyl acrylamide and butyl acrylate copolymer in the mixture is 10:2:1; heating the sludge to 220-300 degrees C, and spraying a liquid including low molecular weight aromatic hydrocarbons and water on the sludge using an evaporation tower, and transferring the remaining sludge containing heavy oil to a supercritical fluid extraction kettle; adding supercritical carbon dioxide and a mixture of propane and isopentane with a mass ratio of 4-10:1 into the kettle as an extracting agent, and extracting heavy oils from the sludge at an extracting temperature of 30-70 degrees C and at a pressure of 7.6-30 MPa; filtering the extracted liquid using a filter, and transferring the solid residue into a supercritical cracking reactor; and performing a catalytic cracking of heavy oil form the sludge in the cracking reactor using a catalyst to extract heavy oil, where the catalyst is zeolite supported metallocene catalyst or an inorganic acid.