The development of sodium ion batteries (SIBs) is greatly restricted by the unsatisfactory anode materials with low capacity and poor cycling stability. Herein, we report a dual-activation hydrothermal process to prepare highly porous activated loofah sponge carbon (ALSC) and ALSC/Ni composite. ALSC is prepared by a facile KOH-based hydrothermal method and further embedded with Ni nanoparticles to form ALSC/Ni composite material by a simple NiCl2-treated hydrothermal pyrolysis. The as-obtained ALSC/Ni composite material has a 3D connected porous structure and a large specific surface area of 689.6 m2 g−1 due to the etching reaction between NiCl2 and carbon. Moreover, higher electrical conductivity and more active sites are achieved in the ALSC/Ni composite material. When applied as anode for sodium ion batteries, the ALSC/Ni electrode delivers a high reversible capacity of 325.4 mA h g−1 and keeps a capacity retention of 72.5% after 100 cycles at 20 mA g−1, much better than ALSC and other counterparts. Due to the unique porous structure and embedded nickel nanoparticles, the designed ALSC/Ni electrode also shows enhanced rate performance. Our work paves a new road for fabrication of high-performance carbon composite electrodes for SIBs.