High-water-content sludge is characterized by high fluidity. The water absorption capacity of waste paper fibers was employed to rapidly reduce the sludge's fluidity, thereby facilitating its transportation and handling. To investigate the effects of waste paper fibers on the fluidity and mechanical properties of solidified high-water-content sludge, flow value tests, UCS (unconfined compressive strength) tests, SEM (scanning electron microscopy), and LF-NMR (low-field nuclear magnetic resonance) tests were conducte. The results indicate that the incorporation of waste paper fibers reduces the flow value of the solidified sludge by 60 ~ 70 mm. The addition of waste paper fibers has a minimal effect on the UCS, but it significantly enhances the toughness of the solidified sludge, with its residual strength and failure strain increasing by 2 ~ 4 times. The improvement in toughness provided by the waste paper fibers decreases as the amount of curing agent increases, and the failure strain exhibits an exponential decay with increasing unconfined compressive strength. The water absorption and swelling of the waste paper fibers facilitate pore filling, reducing the volume fraction of medium pores and increasing the volume fraction of small pores in the solidified sludge. However, with the increase in waste paper fiber content, the volume fraction of small pores decreases. Additionally, a strong linear correlation exists between UCS and small-pore volume fraction.