The present invention relates to a downlink information sending method, the sending method includes: allocating a cell radio network temporary identifier (C-RNTI) and an extension identifier to first user device user device, where a combination of the extension identifier and the C-RNTI is used to identify the first user device; notifying the first user device of the C-RNTI and the extension identifier; scrambling downlink control information (DCI) of the first user device by using the C-RNTI; and sending the scrambled DCI, where the scrambled DCI carries the C-RNTI and the extension identifier, so that the first user device communicates with a network according to the DCI when determining that the notified C-RNTI and the C-RNTI in the scrambled DCI are the same and the notified extension identifier and the extension identifier carried in the DCI are the same.