Abstract: Fourier transform infrared spectrophotometer,elemental analyzer and specific surface area analyzer etc.were utilized to characterize the base PAN(polyacrylonitrile) fiber and its partially hydrolyzed PAN-COOH fiber.The main factors that can affect the strength of base PAN fiber and how its hydrolysis reaction happened in alkaline conditions were discussed.The acidic form hydrolyzed PAN-COOH fiber,having characteristics(on dry basis) strength 9.6 cN/dtex,capacity 0.26 mmol/g,BET area 0.58 m2/g,was prepared.Its production rate from —CN to —COOH,the ways groups of —COOH lining on the surface of the fiber and the possible maximum amounts of —COOH were discussed in detail.