In coal-fired plants, the balance between unburned carbon and NOx emissions stresses the need for rapid and accurate methods for the measurement of unburned carbon. In this paper, molecular ON was adopted to rapidly measure unburned carbon in fly ashes by laser-induced breakdown spectroscopy technique for the first time. The use-of molecular CN overcame the interference between the Fe 247.98 and C 247.86 nm lines and the strong diminishing of the C 193.09 nm line intensity in air. Especially, the multivariate regression method combined with the correction of plasma temperature and self-absorption was used to construct calibration model. The performance of the calibration model was evaluated by the quantitative analysis of unkown fly ashes from different types of coal. The results show that the averaged relative error of prediction and the limit of detection are 0.26% and 0.16 wt %, respectively, while the averaged relative standard deviation is less than 5%. The performance of the quantitative analysis of unburned Carbon meets the requirement of PRC power industry standard and the most of commercial instruments for online or rapidly analysis of unburned carbon.