Abstract: The morphology structure of collagen modified PAN fiber was analyzed by scanning electron microscope. Dyeing；thermodynamics of collagen modified PAN fiber is carried out with Cationic Red X-GRL, including the adsorption isotherm of the fibers，dyeing affinity，heat and entropy, and the data were compared with PAN fiber．The results showed that the adsorption isotherm for Cationic Red X-GRL on collagen modified PAN fiber is a Langmuir-type which is similar to that of PAN fiber．They had much lower dye affinity，dyeing heat and dyeing entropy than PAN fibers when dyed with Cationic Red X-GRL at the same temperature，thus providing some reference for the process design of collagen modified PAN fiber.