This study investigates the scientific and practical feasibility of coal slime co-combustion through thermogravimetric analysis (TGA) and numerical simulation. First, combustion characteristic parameters were determined for 15 types of bituminous and lignite coals, as well as two types of coal slime samples, each prepared with ten different moisture contents, under varying heating rates and particle sizes. The analysis quantitatively revealed that the moisture content of 30% serves as a critical threshold for slime combustion characteristics, beyond which combustion performance drops significantly by 30.50%—45.65%. Under this threshold, co-combustion experiments with slime and nine bituminous coals identified an optimal slime blending ratio of 10%. To address the limited research on slime application in opposed-fired boilers, a 600 MW π-type single-furnace, one-time intermediate reheat boiler was selected for validation.The test results within an error range of 6% were consistent with the simulation results. The study found that the introduction of coal slime can reduce the generation of NO_x, but if the co-combustion ratio is too high, it will cause local excessive SO₂. Overall, the recommended co-combustion ratio of coal slime under the 100%BMCR condition is 10%. Relevant data can provide a good reference for the co-combustion of coal slime.