The beta value of the stock indicates the sensitivity of the portfolio to system risk: the beta value is 1, which means that the stock price will change by the same percentage when the index changes; When the beta value is 1.8, it means that the index changes 1% and the stock price changes 1.8%. When the beta value is 0.5, it means that the index changes 1% and the stock price changes by 0.5%. When the market rises, generally choose a portfolio with high beta value; When the market falls, generally choose a portfolio with a lower beta value to get the best return. Of course, β value is the statistics of historical data, which has certain timeliness and must be considered in application.