Abstract: Abstract：Maize stovers were mixed with sewage sludge at different proportions (0, 25%, 50% and 75%) andtreated in a pyrolysis device up to 600 ℃ via a co-pyrolysis process. Four kinds of biochars (SCB0, SCB25, SCB50and SCB75) were obtained respectively. The properties of biochars, heavy metals (Cu, Zinc, Pb, Ni, Cr, Mn and As)contents, BCR forms and TCLP leaching toxicity characteristics were studied and the potential ecological risks wereevaluated. The results showed that with the increase of maize stover content, the biochar yield, ash content, H/C andN/C ratios were significantly reduced while the pH value and the aromatization degree of biochar were significantlyincreased. After co-pyrolysis with maize stovers, the morphology of heavy metals in the resultant biochar changedsignificantly. The residue fraction ratio of Cu, Zn, Ni and Cr was significantly increased, indicating that pyrolysismight promote the transformation of heavy metals into more stable forms. All the heavy metals leached frombiochars obtained by mixed pyrolysis did not exceed the limit stipulated by GB5085.3-2007 leaching toxicityidentification standard and the overall potential risk index was further reduced . The ecological risk wassignificantly reduced from the moderate to the slight risk level and the minimum risk level reached when theaddition amount of maize stover was 50%. The current study might provide a theoretical basis for the resourceutilization and harmless utilization of sewage sludge and maize stovers.