In this paper, the solid residue and liquid residue were obtained via the hydrothermal processing of sewage sludge. The effect of reaction temperature (180-260 degrees C), retention time (30-90 min), and cosolvent (ethanol volume proportion) (0%-100%) on the polycyclic aromatic hydrocarbons (PAHs) distribution and formation were investigated. The results showed that the concentration of total polycyclic aromatic hydrocarbons (TPAHs) in the solid phase slightly decreased as the temperature increased, while, in the liquid phase, the TPAHs concentration increased; the TPAH concentration decreased from 3.862 mu g/g to 2.808 mu g/g in solid residue, and, in liquid residue, it increased from 2.755 mu g/mL to 2.974 mu g/mL and then decreased to 1.961 mu g/mL. There was no tremendous influence by retention time, since the TPAHs concentration in solid residue decreased from 3.020 mu g/g to 2.808 mu g/g, and, in liquid residue, slightly increased from 1.80 mu g/mL to 1.961 mu g/mL. The concentrations of TPAHs showed the minimum level at 260 degrees C and an ethanol:water ratio of 30:70 (%, v/v), the PAHs with different ring number also showed a decrease at 30%, then an increase at 80%, and finally a decrease at 100%. The conversion pathway of PAHs formation was discussed in this paper: the three parameters exerted the influence on the distribution and formation of PAHs by affected the decomposition and synthesis of organic matters and the mutual transformations of PAHs.