Preparation method of 50K carbon fiber precursor, precursor and carbon fiber

The invention relates to a preparation method of a 50K carbon fiber precursor, the precursor and a carbon fiber, the preparation method comprises the following steps: (1) acrylonitrile, methyl acrylate and itaconic acid are subjected to a water phase suspension polymerization reaction to obtain a polymer, the polymer is terminated through a chelation reaction, and then filtering and drying are performed to obtain a powdery polymer; (2) dissolving the powdery polymer in DMAC (dimethylacetamide) to prepare a spinning solution; (3) enabling the spinning solution prepared in the step (2) to pass through a spinneret plate with the hole number of 49500-50500, spraying at the speed of 13-53m/min, feeding into a coagulating bath, forming to obtain nascent fibers, and washing, oiling, drying, drafting and shaping the nascent fibers to obtain protofilaments; the pressure of the spinneret plate in the step (3) is 800-1600kPa, so that the CV value of the filament density of a monofilament passing through any spinneret pl