Rechargeable sodium-ion batteries (SIBs) with high-area specific capacity and low cost have attracted increasing attention for large-scale energy storage. In this work, Fe₃O₄/FeS₂ heterojunction encapsulated in carbon membrane (FOSM) was rationally designed as freestanding anode for SIBs by taking the waste washcloth as the carbon supporter following calcined at 650 °C (FOSM-650). The porous carbon fiber skeleton inner could support the outer Fe₃O₄/FeS₂ heterojunction to cast excellent flexibility, providing a bridge for fast electron transfer and relieving volume expansion during the charging/discharging process. Meanwhile, the direct contact of outer Fe₃O₄/FeS₂ particles with electrolyte shortened the diffusion path of Na⁺, and the Fe₃O₄/FeS₂ heterojunction can also foster fast electron diffusion at the interface. Therefore, as a freestanding anode of SIBs, the FOSM-650 electrode exhibited a specific capacity of 1.25 mAh cm^-2 at 0.5 A cm^-2 in a half-cell system, 0.5 mAh cm^-2 was achieved even at a high current density of 2 A cm^-2, and still 0.47 mAh cm^-2 was retained after 1000 cycles. Especially, in a FOSM-650//NVP@C full-cell system, the specific capacity was stabilized at 0.58 mAh cm^-2 after 10 cycles at a current density of 2 A cm^-2, 0.21 mAh cm^-2 was still achieved after 1000 cycles. This work not only promotes the development of Fe-based freestanding materials with high area-specific capacity, excellent cycling stability and rate capability, and high energy density for SIBs but also provides an effective and high added-value approach for recycling the waste washcloth for forest protection.