Abstract: In order to ensure the safety of the HVDC converter valve air cooler,a state evaluation method for the air cooler is established based on the entropy weighted gray correlation analysis method. First,a state evaluation index system is established based on the fault location and fault type,where the tube bundles,fans and shutters are the location layer while the appearance,corrosion and insulation faults and fan abnormal noise faults that are strongly related to the operating state of the air cooler are the fault layer,and an index that can accurately reflect the fault is selected as the index layer.Furthermore, the entropy weight gray correlation analysis method is used to determine the index weight;then the index is divided into qualitative indexes and quantitative indexes,and the scoring function of quantitative indexes and qualitative indexes is determined respectively by dividing the index levels.The case analysis is used to verify the validity and correctness of the proposed state evaluation index system.