Abstract: Using the extended positive feedback trading model， a joint test is made on the positive feedback trading in the stock index futures markets of 12 countries. The results show that there is a significant spatial spillover effect of positive feedback trading in the stock index futures markets. Further econometric test in the window period of the Covid-19 pandemic shows that the quantitative easing policies implemented in those countries have curbed the crash of stock markets， but also intensified the spatial spillover effect of positive feedback trading in the stock index futures markets through interest rate channel and inflation channel. Therefore， we should be alert to the risk of market bubble induced by the “overcorrection” of anti-pandemic measures during the Covid-19 period.

Key words: stock index futures; positive feedback trading; spatial spillover effect; quantitative easing