The present invention provides a fiber raw material processing system and its operation method. The fiber raw material processing system is composed of a cutting module, a bulk pulping module, a salt slurry processing module, a pressure screen, a separation module, an inclined screen module, and an extrusion module and a recycling module, which are connected in series. The operating method of the fiber raw material processing system is to process absorptive articles such as diapers or sanitary napkins, etc., which are retained and made into fluff fiber raw materials through the purification and separation steps performed by the modules of the fiber raw material processing system.