In coal-fired plants, Unburned carbon (UC) in fly ash is the major determinant of combustion efficiency in coal-fired boiler. The balance between unburned carbon and NOx emissions stresses the need for rapid and accurate methods for the measurement of unburned carbon. Laser-induced breakdown spectroscopy (LIBS) is employed to measure the unburned carbon content in fly ash. In this case, it is found that the C line interference with Fe line at about 248 nm. The interference leads to C could not be quantified independently from Fe. A correction approach for extracting C integrated intensity from the overlapping peak is proposed. The Fe 248.33 nm, Fe 254.60 nm and Fe 272.36 nm lines are used to correct the Fe 247.98 nm line which interference with C 247.86 nm, respectively. Then, the corrected C integrated intensity is compared with the uncorrected C integrated intensity for constructing calibration curves of unburned carbon, and also for the precision and accuracy of repeat measurements. The analysis results show that the regression coefficients of the calibration curves and the precision and accuracy of repeat measurements are improved by correcting C-Fe interference, especially for the fly ash samples with low level unburned carbon content. However, the choice of the Fe line need to avoid a over-correction for C line. Obviously, Fe 254.60 nm is the best choice for the correction of the C-Fe interference.