Embodiments of this application disclose a cell access method and a device, to provide a network slice service area identifier and network slice configuration information for a terminal device, so that the terminal device accesses a target cell. The method in the embodiments of this application includes: sending, by a serving access network device to a target access network device, a node addition request message to request the target access network device to allocate a resource for multi-connection operation for a terminal device; sending, by the target access network device to the serving network device, the an addition request acknowledgement message; sending, by the serving access network device, a radio resource control (RRC) connection reconfiguration message to the terminal device; receiving, by the serving access network device, a RRC connection reconfiguration complete message from the terminal device; and sending, by the serving access network device, a message indicating that the terminal device has completed the radio resource configuration.