The application provides a data transmission method and a related device. The data transmission method includes: determining, by a first radio access network node, first allocation information when a target radio access network node is the first radio access network node; or, when the target radio access network node is a second radio access network node, instructing, by the first radio access network node, the second radio access network node to determine second allocation information; or, when the target radio access network node is the first radio access network node and a second radio access network node, determining, by the first radio access network node, third allocation information and fourth allocation information.