There was a direct link between the control technology of the polymerization process and the performance of the virgin carbon fiber by using a continuous polymerization process to produce PAN fiber in the engineering production. In this way a series arrangement of three reactors in continuous polymerization process for preparing the PAN was studied. The reaction temperature was a main polymerization factor in the terpolymer system with the acrylonitrile (AN), itaconic acid (IA) and 2-Acrylic amino-2-methyl propane sulfonic acid (AS) as co-monomers between the monofilament mechanical properties of the PAN fiber. The results showed that polymerization temperature can directly affect the intrinsic viscosity and the specific viscosity of the spinning solution, which further affect the structure and properties of the fiber obtained by spinning. With the polymerization temperature decreased gradually, the specific viscosity of the spinning solution increased gradually, while the fiber strength had increased and then decreased. When the reaction temperature was low to a certain temperature, the spinning solution viscosity had increased rapidly, which resulted a deterioration of the spinning process and affected the normal engineering production.