The stock index basis refers to the difference between the stock index futures price and the spot index price. Stock index basis usually reflects the market's expectations for future trends and can help investors grasp and control market risks.

First of all, the stock index basis is an important indicator of stock market risk. When the stock index basis rises significantly, it indicates that the market's bullish expectations for the future have increased, and investors will buy more futures to obtain higher returns. On the contrary, when the stock index basis decreases, it means that the market is not optimistic about the future trend, and investors tend to be cautious and hold spot stocks to avoid market risks.

Secondly, stock index basis can help investors control risks. Investors can use the fluctuations in the stock index basis to perform hedging operations, that is, to open positions in the opposite direction between futures and spot prices to reduce market risks and avoid unexpected losses. In addition, by rationally utilizing the predictive effect of stock index basis, investors can also adjust their investment strategies and allocate assets more scientifically.

Finally, the stock index basis can also provide investors with reference value. By observing and analyzing stock index basis, investors can understand market expectations and trends and scientifically choose investment time and direction. At the same time, the stock index basis can also stimulate investors' independent thinking and action capabilities, and guide them to participate in the investment operations of the stock market in a healthy and rational manner.