Concerning the problems of centralized functions of notary nodes and low cross?chain transaction efficiency in notary mechanism， a cross?chain interaction safety model based on notary groups was proposed. Firstly， notary nodes were divided into three kinds of roles， i.e. transaction verifiers， connectors and supervisors， and multiple transactions with consensus were packaged to a big deal by transaction verification group， and the threshold signature technique was used to sign it. Secondly， the confirmed transactions were placed in a cross?chain wait?to?be?transferred pool， some transactions were selected randomly by the connectors， and the technologies such as secure multiparty computation and fully homomorphic encryption were used to judge the authenticity of these transactions. Finally， if the hash values of all eligible transactions were true and reliable as well as verified by the transaction verification group， a batch task of multiple cross?chain transactions was able to be continued by the connector and be interacted with the blockchain in information. Security analysis shows that the proposed cross?chain mechanism is helpful to protect the confidentiality of information and the integrity of data， realizes the collaborative computing of data without leaving the database， and guarantees the stability of the cross?chain system of blockchain. Compared with the traditional cross?chain interaction security model， the complexity of the number of signatures and the number of notary groups that need to be assigned decreases from O ( n ) to O ( \mathrm{1} ) .