In this paper, a single particle (400–500 μm) co-combustion method was proposed to study the co-combustion characteristics of sewage sludge (SS) and bituminous coal (BC) in air and oxy-fuel conditions. In addition, the thermogravimetric analysis experiments were also carried out for comparison. The results from single particle combustion experiments indicate that SS and BC and their blends all exhibit a two-stage combustion process. With the blending ratio of SS increasing from 0–50 wt %, the volatiles flame of blended fuel particle becomes shorter and smaller, while the average temperature of volatiles flame increases from 1332.4 to 1399.2 °C, which suggests a synergistic effect exists. Owing to the extremely low fixed carbon content of SS, the average temperature of char combustion of the blended fuel particles decreases from 1472.3 to 1281.3 °C. The ignition delay time and volatiles burnout time of the blended fuel particles obviously decrease with the addition of SS. Replacing N2 by CO2 extends the ignition delay time and volatiles burnout time, and decreases the brightness, size, and average temperature of volatiles flame (by more than 140 °C), while its influence on the temperature of char combustion is less obvious. Increasing the O2 mole fraction in CO2 from 21% to 40% shortens the ignition delay time and volatiles burnout time, while it increases the combustion temperatures of volatiles (from 1258.7 to 1501.0 °C) and chars (from 1245.1 to 1545.9 °C).