There are always noticeable problems in the port low-voltage distribution design. For example, instantaneous protection of the incoming circuit-breaker for the transformer can’t meet protection selective requirements, cable sections of L.V switchgears are too small, distribution circuits violate the mandatory provisions,error selections of residual current operated protective devices, and etc. Taking engineering projects as study cases,this paper analyzes the reasons for the design errors, and puts forward train of thought and countermeasures, serving as a reference for port electrical designers.