This standard specifies a method for the determination of carbon content in carbon fibres by combustion absorption method. It is applicable to carbon fibres and products, including carbon fibre tow, filament, staple fibres, woven fabrics, woven and knitted fabrics, etc. The sample pretreatment involves removing the infiltrating agent and drying it, and then crushing it to less than 0.5mm. Reagents include lead chromate, filament oxidized copper, silver wire roll, copper wire roll, alkali asbestos, granular manganese dioxide and tungsten trioxide. Carbon dioxide produced by absorption by the absorber, the mass fraction of carbon is calculated.