Method for preparing polyacrylonitrile carbon fiber precursor

The invention relates to the field of organic polymer, and in particular to a method for preparing polyacrylonitrile carbon fiber precursor. Acrylonitrile and comonomer are subjected to solution copolymerization to form a polymer spinning dope with a relatively even and controllable molecular structure; the spinning dope is subjected to demonomerization, deaeration and multistage filtering, so as to prepare the polyacrylonitrile-based carbon fiber precursor through a wet or dry-wet spinning technology. The key technique of the method is to add a buffer on a pipe from an outlet of a spinning metering pump to an entrance of a spinneret plate assembly; and the buffer is provided with an elastic rubber body, so as offset 50-70% of flow pulsation of the spinning metering pump. The polyacrylonitrile precursor prepared by the invention has small long-range linear density dispersion coefficient; carbonized carbon fiber has substantially reduced long-range linear density dispersion coefficient, so as to lower long-range dispersion coefficient of mechanical properties of carbon fiber (such as tensile strength, elongation at break and tensile modulus, etc.) and improve stability of the batch.