Abstract: The output of sludge and slime is large, and both have the characteristics of high water and high ash. The sludge is particularly prone to ignition due to its elevated volatile matter, while coal slime can maintain combustion with a relatively higher fixed carbon content and the co-combustion and disposal of these two materials present substantial advantages. This study explores nitrogen oxide release characteristics of a typical industrial sludge（DL） and Lingshi coal sludge（LSS） during individual combustion and co-combustion with varying mixing ratios in a vertical fixed-bed reaction system. The results show that the main forms of nitrogen in DL are pyrrole nitrogen（N-5）, protein nitrogen（N-P） and pyridine nitrogen（N-6）, while the main forms of nitrogen in LSS are nitrogen oxide functional groups（N-X）, pyrrole nitrogen（N-5） and protolated pyridine nitrogen（N-Q）. When the two fuels are burned separately, the NO conversion rate of LSS is 6～30 times that of DL, and there is an interaction between the two fuels. The completion time of NO release in the 1∶1 mixed combustion is earlier than that in the separate combustion. The mixing ratio also has a significant effect on the release of NO.When the mixing ratio of DL is 20%, it can inhibit the release of NO.