Abstract:      The presence of polycyclic aromatic hydrocarbons (PAHs) in sludge limits the soundness and recycling of sludge. This study used gas chromatography-mass spectrometry and ratio method to analyze the content and source of 16 PAHs prioritized by the U.S. Environmental Protection Agency, and specially investigated the content and risk changes of PAHs during aerobic composting of deeply dehydrated sludge, and is expected to provide basic data and technical support for improving the risk reduction of pollutants by aerobic composting. The results showed that 16 PAHs were all detected in 6 groups of sludge used for aerobic composting, and their total concentration ranged from 823.07 to 1870.30 ng/g. They were mainly composed of medium and high cyclic PAHs, and mainly from mixed sources of petroleum pollution and combustion. After 28 days of aerobic composting, the total concentration of PAHs in the sludge decreased to 541.19-1456.19 ng/g, corresponding to 13.89~54.29% degradation. The addition of back mixing of the compost products with large particle size could improve the sludge aeration, which was conducive to the degradation of PAHs. Risk entropy was used to evaluate the risk changes of PAHs in sludge before and after aerobic composting, and the overall risk of PAHs before composting was in the medium to low level. Except for the risk of BaP in composting group 1 and Flu in composting group 2 increased from the low to medium level, the risk of PAHs in all composting groups remained unchanged or decreased after aerobic composting. Our finding indicates that PAHs in sludge should be routinely monitored as an important indicator to avoid cumulative ecological risks caused by long-term exposure.