HHI stands for Herfindal-Hirschman Index, abbreviated as hershey Index. Since 1982, the US Department of Justice and the Federal Communications Commission have adopted this index as the basis for antitrust. It is the sum of the squares of the percentage of market share of all market players. If an enterprise monopolizes the market, that is, it has a market share of 100%, and the square of 10000 is 10000, then if it monopolizes the market, this index is10000; Its minimum value is 0, that is, the market is in a state of complete competition. Between 0 ~ 10000, it is divided into three States: HHI is less than 1000, which is a competitive market; HHI is between 1000- 1800, belonging to a moderately concentrated market; HHI is greater than 1800, which is a highly concentrated market.