Short-selling stock index futures means that investors are pessimistic about the future price trend of stock index futures, thinking that prices will fall and may short. Under the background of economic downturn and increasing uncertainty, many investors began to worry about the prospects of the stock market, so they chose stock index futures to be bearish.

First of all, the slowdown or stagnation of global economic growth, especially the continuous escalation and increased uncertainty of the Sino-US trade war, has caused investors to worry about the economic prospects. At this time, the market sentiment is depressed, and the short-selling operation of stock index futures can be described as a good recipe.

Secondly, the direction of the central bank's monetary policy will also affect the trend of stock index futures prices. If the central bank tightens monetary policy, market liquidity will deteriorate, economic growth will also slow down, and the bearish momentum of stock index futures may strengthen.

Finally, the technical disadvantage is also one of the reasons why stock index futures are bearish. For example, the moving average and MACD in technical indicators indicate that the trend of stock index futures prices is falling, and this bearish expectation will be more common in the market.

To sum up, shorting stock index futures is a risky strategy, but it is also an investment choice. Although investors need to consider various risks, they can still win profits in the market through scientific analysis and decision-making.