Abstract：Maize stovers were mixed with sewage sludge at different proportions (0, 25%, 50% and 75%) and treated in a pyrolysis device up to 600 ℃ via a co-pyrolysis process. Four kinds of biochars (SCB0, SCB25, SCB50 and SCB 75) 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 were evaluated. The results showed that with the increase of maize stover content, the biochar yield, ash content, H/C and N/C ratios were significantly reduced while the pH value and the aromatization degree of biochar were significantly increased. After co-pyrolysis with maize stovers, the morphology of heavy metals in the resultant biochar changed significantly. The residue fraction ratio of Cu, Zn, Ni and Cr was significantly increased, indicating that pyrolysis might promote the transformation of heavy metals into more stable forms. All the heavy metals leached from biochars obtained by mixed pyrolysis did not exceed the limit stipulated by GB5085.3-2007 leaching toxicity identification standard and the overall potential risk index was further reduced . The ecological risk was significantly reduced from the moderate to the slight risk level and the minimum risk level reached when the addition amount of maize stover was 50%. The current study might provide a theoretical basis for the resource utilization and harmless utilization of sewage sludge and maize stovers.