Embodiments of the present invention provide a dual-connectivity (DC) establishment method and device. The first DC architecture includes a Master Node (MN) and a Secondary Node (SN), wherein the SN includes a Central Unit (CU) and a Distributed Unit (DU); and, the CU includes a Control Plane functional entity (CP) and a User Plane functional entity (UP). The method includes steps of: receiving, by an SN-CP, a first SN setup request message transmitted by an MN; transmitting a first resource setup request message to an SN-UP according to the first SN setup request message, and receiving a first resource setup response message transmitted by the SN-UP; and, transmitting, by the SN-CP, a first bearer setup request message to an SN-DU, and receiving a first bearer setup response message transmitted by the SN-DU.