The earthing design of power distribution system in port project is an important work of the port electrical design.Reasonable earthing design of power distribution system is of great significance to safety (personal safety and equipment safety),reliability and economy of port electrical engineering.However,the earthing system is complex and difficult to understand and grasp,and there are often hidden safety hazards in design documents.In this paper,according to the different earthing modes of 10 kV power grid (unearthing or earthing by small resistance),the earthing design of port distribution system is analyzed to deepen the understanding of earthing system and provide help for the earthing design of port distribution system.