The invention relates to a data covert transmission method based on a block chain network, and belongs to the technical field of data covert transmission. According to the method, a public key servingas a certificate of covert communication is exchanged through an out-of-chain key exchange stage; then constructing a special transaction which contains a message encrypted by a sender private key and can leak signature information of the sender private key and is generated by using a Kleptography technology through a covert data construction stage; then, the special transaction is propagated through an in-chain data transmission stage; and finally, reading and detecting each block chain transaction propagated in the block chain network one by one by a receiver in a hidden data extraction stage, and if the signature data in the transaction can extract a private key by using a Kleptograpy technology, indicating that the transaction is a special transaction carrying encrypted data. And thereceiver decrypts the original text by using the extracted private key. Compared with the prior art, the method has the characteristic of high concealment, and an enemy cannot identify a concealed channel according to account characteristics.