Embodiments of this application provide a blockchain-based data processing method, a device, and a medium. The method includes: sending a first channel closing message on a chain-off channel; receiving a second signature in a second state and a second channel closing message that are sent on the off-chain channel, where the second signature is obtained by signing the second channel closing message; and signing a third channel closing message to obtain a first signature in the second state, and sending the first signature. This application can ensure transaction security and improve a transaction processing capability.