Charging pumps are crucial safety equipment in nuclear power plants. Their failure can lead to reactor state regression and even emergency trips. Currently, many nuclear power plants encounter issues with the low reliability of charging pump gear couplings. Premature failure of these couplings can cause excessive vibration in charging pumps, violating relevant monitoring requirements and rendering the pumps inoperable. Extensive analyses, including coupling installation review, coupling design verification, manufacturing quality analysis, grease quality analysis, and coupling damage morphology analysis, have been conducted on gear couplings. This paper explores the failure of gear couplings from multiple perspectives to determine the causes of their low reliability. The analyses reveal that the low reliability of charging pump gear couplings is attributed to their design and manufacturing qualities. Consequently, solutions to address the low reliability of gear couplings are proposed.