Hard carbon (HC) materials are considered as promising anode materials for sodium-ion batteries (SIBs) due to their advantages of high capacity, low working potential, and low cost. The most important feature of HC materials is a rich microcrystalline structure that is conducive to the sorption and insertion/extraction of sodium ions, which in turn enables HC materials to exhibit a superior sodium ion storage performance. However, HC materials have some problems such as low initial Coulombic efficiency (ICE), insufficient long-cycle stability, and poor rate performance in the application. A functional design can be an effective strategy to improve these problems of HC. This review mainly summarized recent studies on the modification of HC anode for SIBs, and provided the related information on some typical optimization strategies and the latest research progress in the functional design of HC anodes. The advantages and disadvantages of functional design were also discussed, providing a theoretical basis and technical support for guiding the commercial application of HC anodes for SIBs.