The stock price index is an index that describes the changes of the overall price level of the stock market. It is to select a group of representative stocks, weight and average their prices, and get them through certain calculation. The specific stock selection and calculation methods of various indexes are different.

For example, the Shanghai Composite Index is weighted by the number of shares issued by sample stocks (stocks included in the index calculation range), and the calculation formula is: reporting period index = (total market value of constituent stocks in the reporting period/base period) × base period index, where total market value = σ (stock price × number of shares issued).

Stock indexes can be bought and sold, which involves stock index futures (refers to standardized futures contracts with stock indexes as the subject matter, and both parties agree to buy and sell the subject index at a certain date in the future according to the pre-determined stock index size), but the required funds are relatively large.