In order to understand the effects of Solid Recovered Fuel (SRF) blending on the thermal reaction characteristics and flue gasenvironmental characteristics of sludge incineration disposal. The thermogravimetric law, comprehensive burning characteristic index, slagging characteristic and NOx emission characteristic of SRF and sludge mixed combustion process under different mixing ratio were analyzedby using thermal synthesis analyzer, SEM, XRD and GA-21plus flue gas analyzer. The results show that there are obvious multi-peakweight loss phenomena in the mixed firing process, mainly concentrated at 192.3-645.3 ℃ . At 11% blending ratio, the maximum weightloss rate reaches 0.14% / min, which is significantly higher than that of sludge incineration alone. With the increase of SRF blending ratio,the ignition temperature and burnout temperature of the fuel decrease, and the full combustion stage shifts to the low temperature region.When the SRF mixing ratio is 11%, the stable combustion performance index and comprehensive combustion performance index are increased by 1.38 times and 1.17 times, respectively, which improves the ignition characteristics of sludge incineration alone. In addition,after SRF mixing, the melting temperature of fuel ash increases, the adhesion degree of ash decreases, and the agglomeration strength ofparticles decreases, thus weakening the slagging situation when the sludge is incinerated alone. However, the mixed combustion leads toan increase in NOx emission in the flue gas.