After the stock index futures enter the delivery period, the margin will gradually increase. Because the closer the delivery is, the clearer the futures price is relative to the spot, and the unfavorable party may default, so it is necessary to increase the margin to make it gradually higher than the liquidated damages, so that it is not afraid of default.

Delivery of stock index futures: according to the difference between the "price" of your futures contract and the actual "price" of the current spot market, it is equivalent to closing the position at the spot "price" on the delivery date. Stock index futures are delivered in cash.