Changes in trading volume and open interest can reflect the activity of contract trading and investors’ expectations. The changes in trading volume and open interest have the following relationship: First, only when new buyers and sellers enter the market at the same time, open positions will increase and trading volume will increase at the same time. Second, when one of the buyers and sellers closes a position (i.e. changes hands), the position remains unchanged, but the trading volume increases. This includes both long and short changes of hands. Third, when both the buyer and seller are original traders and both parties close their positions, the position will decrease and the trading volume will increase. By analyzing changes in open positions, we can know whether funds are flowing in or out of the market.