The microwave thermal conversion process of oil sludge was studied. It was found that the microwave thermal conversion process of oil sludge consisted of 5 stages: rapid heating, microwave drying, microwave hydrocarbons evaporation, microwave pyrolysis and microwave calcining. Using the residue produced from the microwave thermal treatment of oil sludge as a microwave absorbent can significantly accelerate the conversion. However, it does not show significant effect on the features of microwave thermal conversion. Meanwhile, the addition of residue at appropriate percentages increased oil recovery rate. The non-condensable gases consist of H2 and C1~C5 hydrocarbons. The recovered oil was mainly produced at microwave evaporation and microwave pyrolysis stages, consisting of 89% light oil and 11% heavy oil.