Method for preparing polyacrylonitrile-based carbon fiber precursor fiber

The invention provides a preparation method for polyacrylonitrile base carbon fiber protofilament. ammonium persulfate-ammonium sulfite or ammonium hydrogen sulfite is used as the aqueous phase suspension copolymerization of a initiation system for preparing polyacrylonitrile base carbon fiber protofilament which uses polymers as raw materials; polymers are made into 16-20Wt percent of slurry at -18-0 DEG C, vacuumized to 40-95 Kpa and dissolved for 1-2 hours at 40-55 DEG C; then spinning stock solution at 70-80 DEG C is extruded into a spinning pipe in coagulation bath via a spinneret to be shaped, and PAN nascent fiber is obtained through the minus elongation of the coagulation bath; the PAN nascent fiber has desolventize flushed away by hot water, and is simultaneously stretched, oiled, dried for densification, baked and elongated to obtain PAN base protofilament, and the tensile strength is no lower than 6.60N/dtex; the carbon fiberstrength is 3.30-4.01Gpa, and the elastic modulus is 210-262Gpa. The main technical indexes of the present invention are equivalent to the similar products in America, Japan and other countries.