The theoretical price of stock index futures can be deduced by the definition of basis. According to the definition, basis = spot price-futures price, that is, basis = (spot price-futures theoretical price)-(futures price-futures theoretical price). The former part can be called theoretical basis, which mainly comes from holding cost (regardless of transaction cost, etc.). ); The latter part can be called value basis, which mainly comes from investors' overestimation or underestimation of stock index futures prices. Therefore, in general, the theoretical basis must exist before the expiration of the contract, but the value basis does not necessarily exist; In fact, in the case of market equilibrium, the value base is zero.