This topic studies the concept and classification of arbitrage. Arbitrage refers to the trading behavior of using the price difference between related markets or related contracts to trade in the opposite direction in order to profit from the favorable change of price difference. If the spread between the futures market and the spot market is used for arbitrage, it is called spot arbitrage; If the spread between different contracts in the futures market is used for arbitrage, it is called spread trading or hedging profit. According to the different futures contracts selected, spread trading can be divided into intertemporal arbitrage, cross-variety arbitrage and cross-market arbitrage. Intertemporal arbitrage refers to buying and selling futures contracts of the same commodity in different delivery months in the same market (the same exchange), so as to hedge these futures contracts at favorable opportunities and make profits at the same time. Cross-variety arbitrage refers to arbitrage by using the price difference of futures contracts between two or three different but interrelated commodities, that is, buying or selling interrelated commodity futures contracts at the same time in a certain delivery month, in order to hedge and close these contracts at the same time at a favorable opportunity. Cross-market arbitrage refers to buying (or selling) a commodity contract in a certain delivery month on one exchange and selling (or buying) the same commodity contract in the same delivery month on another exchange, in order to hedge the contracts of two exchange rivals at the same time at a favorable opportunity. (P 127~ 128)