Fly　ash　contents　can　be　considered　as　a　basis　for　optimal　and　stable　boiler　combustion　control　and　fly　ash　quality　control　in　power　plants,　especially　the　unburned　carbon　in　fly　ash.　The　real-time　and　quantitative　measurement　of　the　contents　in　fly　ash　was　studied　using　a　constructed　two-stage　cyclone　measurement　system　and　detected　using　the　laser-induced　breakdown　spectroscopy　(LIBS)　technique.　The　surrounding　gas　effect,　such　as　the　CO2　effect　on　the　unburned　carbon　content,　was　studied　comprehensively　in　this　paper.　The　CO2　effect　was　eliminated　using　this　proposed　combination　method　of　a　two-stage　cyclone　measurement　system　and　LIBS　with　a　1　ns　pulse-width　laser　according　to　the　efficient　gas-particle　separation　and　the　controlled　laser-induced　plasma　processes　of　particle　flow.　The　quantitative　analysis　was　improved　using　the　plasma　temperature　correction　method,　with　the　intensity　ratio　of　the　emission　pair　from　magnesium　as　the　plasma　temperature　indicator.　The　measurement　of　the　unburned　carbon　content　in　fly　ash　with　the　temperature　correction　method　presented　the　concordant　results　analyzed　by　the　chemical　analysis　method.　The　feasibility　and　improved　detection　ability　for　the　real-time　measurement　of　fly　ash　contents　in　power　plants　are　demonstrated.