Cobalt (Co) has advantages such as low electrical resistivity, good thermal stability, and strong adhesion to copper (Cu), which makes it a new barrier layer material that can replace tantalum (Ta) for copper interconnect structures in integrated circuits (ICs) with technology nodes below 14 nm. Chemical mechanical polishing (CMP) is the only method that can achieve both local and global planarization of copper interconnects, and it is also a key technology that determines the reliability of cobalt-based copper interconnect ICs. Citric acid contains hydroxyl groups that have a strong chelating effect on metal ions after ionization, and has become the main complexing agent in CMP and post cleaning of cobalt-based copper interconnect. The application and research progress of citric acid in copper interconnect CMP and post cleaning are reviewed in this paper, including the effect of citric acid on Cu/Co removal rate (RR) selectivity, the surface morphology of Co and the removal of residue on the Co surface in post Co CMP cleaning. The development trend of complexing agent and barrier layer CMP of copper interconnection is prospected.