The present disclosure discloses a data communication method and a device, to resolve a prior-art problem of a high latency for switching a terminal device from an idle mode to a connected mode. The method includes: prestoring, by a terminal device, a TA indication list of a group of cells; performing, by the terminal device, cell selection or reselection, and obtaining a cell identity of a cell obtained after the selection or reselection; querying, by the terminal device based on the cell identity, the TA indication list of the group of cells for a TA value corresponding to the cell identity; and if the terminal device successfully finds, in the TA indication list of the group of cells, the TA value corresponding to the cell identity, sending, by the terminal device, an uplink Radio Resource Control (RRC) message in a random access-free manner.