SouthEX is the first decentralized exchange based on EOS. SouthEX combines on-chain smart contract with off-chain matchmaking engine. In placing an order, the user pays the order amount with wallet directly. The on-chain smart contract escrows the order amount, and the off-chain matchmaking engine matches the order efficiently. Moreover, it employs on-chain and off-chain dual verification. After closing the deal, the smart contract will transfer the amount to wallet directly. In realizing the efficient matchmaking efficiency of the centralized exchange, SouthEX can dramatically reduce the quantity and time of the encrypted currency the user escrows in the exchange as well at the same time, so as to balance high efficiency and security.