the so-called sector is a kind of stock with the same or similar industry background. Why should stocks be classified? One is for the needs of statistical analysis. For example, China's Shanghai and Shenzhen stock market classification index divides all the stocks in the stock market into five sectors: industry, commerce, real estate, comprehensive and public undertakings. The rise and fall of the stock market can only provide the overall level of the stock market, but can not provide a more detailed overview. The second is to analyze the needs of companies in different industries. The rise and fall of a certain kind of stock can not be separated from the change of the company's fundamentals, and the change of the company's fundamentals is closely related to the development prospects of its industry. It is convenient for everyone to choose stocks according to the industry, and then carry out cross-industry investment portfolio. The third is the atmosphere created by the main market forces. In order to attract the popularity of the follow-up market, the main force usually pulls up a certain type of stocks and focuses on individual varieties. Therefore, the plate is also the product carefully cultivated by the main market forces. For the majority of retail investors, it is impossible to study all of them in the face of thousands of stocks. If we narrow our attention to a certain sector and then make a more detailed analysis of the stocks in that sector before making a decision, I am afraid the probability of success is much greater. Usually, all stocks in the stock market can be divided into different sectors according to different standards. Sometimes, a stock is divided into multiple sectors because it has two or more characteristics at the same time. At this time, the division of sectors overlaps, that is, the same stock can be classified into different sectors according to different standards. Although there are various standards for the division of plates, they can basically be summarized into two standards, namely, the standard for the division of industry characteristics and the standard for the division of market characteristics.