Current blockchain systems have high requirements on network connection and data transmission rate, for example, nodes have to receive the latest blocks in time to update the blockchain, nodes have to immediately broadcast the generated block to other nodes for consensus, which restricts the blockchain to run only on real-time connection networks, but the existence of delay tolerant networks poses a great challenge to the deployment of blockchain systems. To address this challenge, a novel blockchain transaction mechanism is proposed. First, the block structure is modified by adding a flag, and on this basis, the definition of the extrachain is proposed. Secondly, based on the blockchain transaction process, transaction verification and consensus algorithms on the extrachain are presented. Thirdly, both the extrachain selection algorithm and appending algorithm are proposed, so that the extrachain can be appended to the blockchain fairly and safely. Finally, an extrachain transmission scheme is presented to broadcast the blocks generated in the delayed network to the normal network. Theoretical analysis and simulation experiments further illustrate the efficiency of the proposed mechanism.