Abstract: As an important part of the transmission and distribution network,the reliability of power cable determines whether the whole power system can operate safely and reliably.In order to accurately characterize the operating state of power cables,it is particularly important to select appropriate online monitoring and condition assessment methods.At present,there are many kinds of on-line monitoring methods for power cables,and their basic principles,main functions and positioning accuracy are different.In order to compare and analyze the advantages and disadvantages of different online monitoring methods,and further improve the level of cable on-line monitoring technology and cable fault location accuracy,this paper reviews the on-line monitoring and diagnosis technology of non-electrical parameters and electrical parameters of power cables and various methods of power cable condition assessment in recent years.In addition,this paper also describes the detection method for the ablation fault of the water-blocking buffer layer.Finally,the shortcomings of on-line monitoring in measurement methods,measurement accuracy and fault location,as well as the corresponding optimization and improvement methods are summarized,and the countermeasures for the ablation failure of water-blocking buffer layer are prospected.