The invention discloses large tow polyacrylonitrile pre-oxidized fiber, large tow carbon fiber, and preparation methods of the large tow polyacrylonitrile pre-oxidized fiber and the large tow carbon fiber. The preparation method of the large tow polyacrylonitrile pre-oxidized fiber comprises: 1, after an electron accelerator is turned on, carrying out a continuous irradiation reaction on large towpolyacrylonitrile fiber, wherein the irradiation absorption dose rate is 50-2*10<6> Gy / s, and the total irradiation absorption dose is 20-3000 kGy; and 2, carrying out pre-oxidation on the irradiatedlarge tow polyacrylonitrile fiber for 15-75 min at a temperature of 180-280 DEG C so as to obtain the large tow polyacrylonitrile pre-oxidized fiber, wherein the large tow polyacrylonitrile pre-oxidized fiber is carbonized to obtain the carbon fiber. According to the present invention, with the preparation method, the heat release during the pre-oxidation of the polyacrylonitrile fiber can be significantly reduced, the pre-oxidation temperature can be reduced, the energy consumption can be reduced, and the oxygen is introduced so as to solve the oxygen diffusion problem and reduce the pre-oxidation time; and the large tow polyacrylonitrile pre-oxidized fiber has advantages of high density and high strength, and the subsequently-prepared carbon fiber material has excellent performance.