The term "back-to-back" refers to the inconsistency between the futures price and the spot price. Generally speaking, futures prices are related to spot prices because they trade the same asset. However, due to market supply and demand, investor sentiment, policy changes and other factors, futures prices sometimes deviate from spot prices. Deviation is generally divided into positive deviation and reverse deviation. Positive deviation means that the futures price is higher than the spot price, and reverse deviation means that the futures price is lower than the spot price. Possible reasons for the positive deviation include: changes in market supply and demand, strong bulls in futures market, strong sellers in spot market and optimistic investors. The possible reasons for the reverse deviation include: investors are pessimistic about the market, buyers in the spot market are strong, and short positions in the futures market are strong. The current deviation may bring arbitrage opportunities to investors. For example, if the futures price is higher than the spot price, investors can buy assets in the spot market and then sell them in the futures market to make a profit. But this arbitrage opportunity is often short-lived, because once the market returns to equilibrium, the deviation will disappear. When trading futures, investors need to pay attention to the deviation of futures and make corresponding investment decisions according to market conditions.