Orthogonal experimental design (I) and (II) were used to study optimum coagulation technology in wet spinning of high molecular weight PAN nascent fiber. Relationship between shape factor (De) and coagulation conditions such as coagulation bath concentration, temperature, and minus draw ratio was investigated to obtain nascent fiber with the minimum De value and smooth surface morphology. The nascent PAN fiber fabricated at the conditions of 80 wt% coagulation bath concentration (in this paper, the coagulation bath concentration refers to the mass concentration of DMSO in coagulation bath), 0 % minus draw ratio, and $40^{circ}C$ coagulation bath temperature has the smallest fiber diameter, the most circular cross sectional (minimum shape factor) and smooth surface morphology, and the maximum density, which resulted in the most excellent mechanical properties of nascent PAN fiber.