In this study, a strategy of combining steam injection with oil sludge ash addition to improve the yield and quality of the oil products of oil sludge pyrolysis process is proposed. Oil sludge pyrolysis with the addition of different amounts of steam and oil sludge ash was conducted under inert conditions at 450 degrees C by employing a stirred tank reactor. This procedure was performed to investigate the effect of steam injection and oil sludge ash addition on the distribution and quality of the oil products. The possible catalytic mechanism occurring during the pyrolysis process was proposed. The quality of the oil product was determined based on the results of the boiling point distribution, the carbon residue, the ultimate analysis, the Saturates, Asphaltenes, Resins and Aromatics (SARA) composition and the Nuclear Magnetic Resonance (NMR) analysis. The results indicate that both steam injection and oil sludge ash addition caused the oil yield to increase. Steam injection increased the proportions of the heavy and middle fractions in the oil product and reduced the carbon residue by improving the stability of the oil system. Oil sludge ash addition reduced the carbon residue and lessened the decrease in the light oil/heavy oil ratio by converting the heavy fraction or coke precursors to lighter fractions. The synergetic effect of steam injection and oil sludge ash addition can further reduce the carbon residue of the oil product. The presence of oil sludge ash significantly reduced the S, N, and O mobilities from the oil sludge feedstock to the oil product. These performances can be further improved by the synergetic effect of steam injection and oil sludge ash addition, which might be attributed to the improved catalytic effect of oil sludge ash by steam injection. (C) 2016 Elsevier Ltd. All rights reserved.