A computer-implemented method for improving security of smart contract comprises: obtaining a first and a second transactions both invoking a smart contract, wherein the first transaction is associated with a protection condition; executing the second transaction and updating a current state of the smart contract; determining whether the updated current state of the smart contract satisfies the protection condition; in response to determining that the updated current state satisfies the protection condition, executing the first transaction, and recording the second and the first transactions into a data block for adding to a blockchain; and in response to determining that the updated current state does not satisfy the protection condition, recording the second transaction into another data block for adding to the blockchain, without executing the first transaction.