Usually, the trend of stock index futures follows the underlying index, but stock index futures will affect the Shanghai and Shenzhen 300 Index to some extent. The specific performance is as follows:

1. Stock index futures are ahead of the rapid upward or downward trend of the index in a short period of time. If it affects investors' mood to a great extent, it will prompt investors to buy and sell stocks of the 300 index, thus affecting the changes of the Shanghai and Shenzhen 300 index.

2. Under the current regulatory level in China, some institutions will first establish corresponding positions in stock index futures, and then influence the trend of the index by buying and selling the constituent stocks of the Shanghai and Shenzhen 300 Index at the key time or point of the trend, so as to make the index run in a direction favorable to its future positions.