The invention relates to a PAN (polyacrylonitrile) carbon fiber fibrillation mass production method. The method includes: winding PAN carbon fiber precursors on a metal tube to allow the metal tube tohave tension to obtain a PAN carbon fiber precursor bobbin; placing the bobbin in reaction kettles for reaction, exhausting air during the reaction prior to feeding CO2 to enable the inner cavity ofthe reaction kettles to be in a supercritical CO2 state, and releasing pressure slowly to obtain modified PAN fiber. The device applied in the method is characterized in that two parallel reaction kettles connected through a pipeline and loaded with supercritical CO2 fluid circulation pumps and pipeline systems thereof are connected with the PAN carbon fiber precursor bobbin, and the reaction kettles are loaded with temperature and pressure regulation systems. The method is simple, easy to operation, moderate in condition, short in time and environment friendly, a great deal of fibers with high strength are obtained, and novel technology and method are provided for preparation of high-performance carbon fibers; the device applied in the method is simple and easy to operate.