Provided are a method, apparatus, and system for transmitting data during a handover procedure, relating to the technical field of mobile communications. The method includes: receiving RRC signaling sent by a source MeNB, herein the RRC signaling carries first resource configuration information corresponding to a target MeNB to be accessed by a terminal and second resource configuration information corresponding to a SeNB already accessed by the terminal; when the terminal leaves a serving cell covered by the source MeNB, according to the second resource configuration information maintaining a radio connection with the serving cell of the SeNB, retaining a protocol layer at the SeNB corresponding to a Split bearer to be unchanged, and initiating a random access to the target MeNB according to the first resource configuration information.