The invention relates to the technical field of big data, block chains and smart contracts, and in particular to a block chain smart contract-based data transaction method. According to the block chain smart contract-based data transaction method, purchase and sale behaviors of purchasers and sellers of transactions are recorded through block chains, automatic execution of the transactions is realized by utilizing smart contracts, and big data for the transactions is not recorded in the block chains and is encrypted and stored in an external data memory, so that the purchasers only can obtain the data after the smart contracts are successfully transacted; and moreover, the purchasers can publish transactions through a supervisory block chain consensus network, so that third-party witness is realized and the security guarantee of data transactions is increased.