A flexible and free-standing multichannel carbon nanofiber (MCNF) film electrode was fabricated through electrospinning and carbonization. After high-temperature treatment of MCNFs in vacuum, the obtained fibers (MCNFs-V) had a dilated interlayer spacing of graphene sheets (0.398 nm) and an ultra-low specific surface area (15.3 m²/g). When used as an anode for sodium-ion batteries, the MCNFs-V showed a discharge plateau below 0.1 V, and sodium was intercalated into the stacked graphene sheets layers during the sodiation process. The MCNFs-V exhibited a reversible and high specific capacity of 222 mAh/g at a current density of 0.1 A/g after 100 cycles and excellent long-term cycling stability, which was superior to that of MCNFs. The improved sodium storage performance was attributed to the unique microstructure of the MCNFs-V with an enlarged interlayer spacing of graphene sheets for sodium intercalation. The MCNFs-V electrode holds great promise as an anode material for commercial sodium-ion batteries.