A rapid measurement of micro-nano carbon particles within complicate combustion media is investigated. Carbon particles from pulverized coal combustion in the pure hydrogen flame are heated by a high-power pulsed laser beam. The size distribution of carbon particles is obtained using a multistage exponential function method to fit time-resolved radiation emitted by the laser-heated particles, where the flow zone is determined by Kn. The results show that three sizes of carbon particles exist and the average diameters are 7 nm, 25 nm, 3 μm, respectively, which correspond to the newly-born soot, mature soot, and char or unburned coal particles. The variations of each kind of carbon particles during coal combustion are investigated according to the size and relative concentration of each particles component versus the flame height. The above method can be used as a tool for rapid detecting size distribution of multi-scale carbon particulates under the high-temperature environment.