Legal basis: The national economic industry classification provides the classification and code of economic activities of the whole society, which is applicable to the classification of economic activities in national macro-management such as statistics, planning, finance, taxation, industry and commerce, and is used for information processing and information exchange. The standard adopts line classification and hierarchical coding method, and divides the national economic industry into four levels: large category, large category, medium category and small category. The code consists of a Latin letter and four Arabic numerals.