Developing electrode materials with high capacity and low cost is crucial for promoting the application of sodium-ion batteries. In this paper, a new Sb–PMA-300 metal–organic framework (MOF) material is synthesized by chelation of Sb³⁺ and pyromellitic acid (PMA) followed by a heat treatment at 300 °C. As anodes for sodium-ion batteries, the Sb–PMA-300 composite exhibits a stable capacity of 443 mA h g⁻¹ at a current density of 0.1 A g⁻¹. At a current density of 1 A g⁻¹, the discharge capacity is maintained at 326.4 mA h g⁻¹ after 200 cycles. The electrode process dynamics of this material are mainly controlled by diffusion. The values of the diffusion coefficient of Na⁺ are between 10⁻¹² and 3.0 × 10⁻¹⁰ cm² s⁻¹ during discharging, while they are between 10⁻¹² and 5.0 × 10⁻¹¹ cm² s⁻¹ during charging. The excellent cycle stability is attributed to the special structure of the MOF material, where the organic ligand prevents the aggregation of Sb alloy particles and buffers the tension resulting from volume variation.