Butterfly arbitrage is a common form of intertemporal arbitrage. It consists of an intertemporal arbitrage and a bear market arbitrage in an intermediate delivery month. Because the futures contracts in recent and distant months are on both sides of the middle month, just like the wings of a butterfly, it is called butterfly arbitrage. Compared with ordinary intertemporal arbitrage, the risk and return of item B are relatively small in theory, but it does not belong to risk-free arbitrage. Item D is a description of cross-variety arbitrage.