Abstract: As an emergency safety power source for nuclear power plants,emergency diesel engines are directly related to nuclear safety. 18 PA6 B emergency diesel engines are widely used in nuclear power plants at home and abroad,and each diesel unit is equipped with at least one daily oil tank. In recent years,the 18 PA6 B emergency diesel engines of many domestic nuclear power plants under construction have experienced daily oil tank spills during commissioning,which has caused hidden fire hazards and affected the progress of the project’s hot trial. This article took the case of an oil spill from a daily oil tank during the commissioning of an 18 PA6 B emergency diesel engine as an example to analyze the root cause and proposes targeted solutions.