Abstract: Because of their excellent mechanical properties, polyacrylonitrile(PAN)-based carbon fibers are widely used in aerospace, general industry, high-end sports goods, etc. High purification and densification of carbon fiber precursors is one of the key techniques for the preparation of high-performance carbon fibers. During the extraction and testing of the residual solvent in carbon fiber precursors, boiling water causes the decomposition of the residual solvent in the dimethyl sulfoxide (DMSO), which seriously affects the accurate quantification of the residual solvent in the fibers. A systematic study of accurate extraction and quantification of residual solvent dimethyl sulfoxide (DMSO) in carbon fiber precursors was carried out at the National Measurement and Testing Center for Carbon Fiber Industry. Water, ethanol, acetone, and cyclohexane were used as extraction agents. The effects of extraction agent types, fiber quality, extraction temperature and time, and measuring instruments on the accurate quantification were studied. The extraction conditions and quantitative testing methods were proposed to provide measurement and testing services for improved process control of the preparation of high-performance fibers.