Polyacrylonitrile (PAN)-based precursor was pre-oxidized at a constant temperature at 180 ~ 260 ℃, and then carbonized at a low temperature at 400~600~ 700  to prepare polyacrylonitrile-based carbon fibers at different carbonization temperatures. The effects of heat treatment temperature on the elemental composition, surface morphology, and mechanical properties of PAN-based carbon fibers were studied by elemental analysis, scanning electron microscopy (SEM), photoelectron spectroscopy, Raman spectroscopy, and monofilm tensile testing. The results show that the carbon content increases from 62% to 74% after heat treatment, indicating that the carbonization stage is the enrichment stage of the c element, and the maximum tensile strength of the monofilament is 824 MPa. At 824 MPa, the degree of graphitization of carbon fiber increases, and the grain size of graphite increases, indicating that the mechanical properties of the fiber are enhanced during the carbonization stage.