With the continuous development and progress of the digital economy, the efficiency and security of data element circulation and transactions have been made key factors for developing the data economy. A data transaction mechanism based on blockchain cross chain technology was proposed, which was based on the blockchain ecosystem, and was centered on the secure transmission of data value. It constructed a data asset value evaluation model, aiming to promote data security exchange and data ecosystem construction. Firstly, by transaction alliances and witness mechanisms, the blockchain data verification, asset valuation, and data ownership confirmation were resolved and the transaction time was reduced. Secondly, the integration of technologies such as cryptography, multi-party secure computation, and Merkel simplified payment verification (SPV) path verification, the privacy, authenticity, and integrity of data transactions was ensured, secure exchange of on chain and off chain data was achieved. Once again, the application of the Black-Scholes(B-S) option pricing model provided scientific guidance for evaluating the value of data assets. At the same time, the relay chain recorded various stages of data transactions, the transparency and non repudiation of the entire transaction process was ensured. Finally, the operational performance of the system was validated in the experimental environment. The design of this mechanism provides new ideas for the secure exchange of data asset value.