The pyrolysis characteristics of sewage sludge, wheat straw and its mixture were studied by nonisotropic thermogravimetric analysis (TGA). In the temperature range of 400 K-950 K, 40 K/min, 45 K/min and 50 K/min heating rate were set respectively, in N2 atmosphere and CO2/N-2 mixed atmosphere. According to the thermal analysis chart obtained from TGA, it was observed the vast majority of mass loss spread at the range of 450-800 K in all samples. The Co-pyrolysis kinetics of sewage sludge and wheat straw was described by a fourth-order DAEM model. It is proved that the model can well match the TG experimental data. The results obtained from the optimized parameters show that the activation of sewage sludge is lower than that of wheat straw, and the activity of the mixture gradually increased with the increase of wheat straw content. The presence of CO2 has a slight inhibitory effect on the pyrolysis of the mixture below 900 K compared to that in an N-2 atmosphere, but with temperature increasing, CO2 will have a secondary reaction with biochar. (C) 2019 Elsevier Ltd. All rights reserved.