A mobility management method performed by a user equipment, UE , wherein the method comprises: receiving , by user equipment, UE, from a first base station, a message used for indicating a primary cell, PCell, change, wherein the first base station is a base station that a source PCell of the UE belongs to, and the message used for indicating a PCell change carries information about a target PCell; performing , by the UE, a PCell change based on the received message used for indicating a PCell change, wherein the PCell change comprises: changing the target PCell to a PCell of the UE and changing the source PCell to a secondary cell, SCell, that is in an active state and that is of the UE, and during the PCell change, the UE continues to perform data transmission with the source PCell and the target PCell; and sending, by the UE, a message used for indicating PCell change completion to the first base station or a second base station , wherein the second base station is a base station that the target PCell belongs to; wherein after the receiving a message used for indicating a PCell change, the PCell change further comprises: determining, by the UE, that the target PCell is not a serving cell of the UE; adding, by the UE, the target PCell as an SCell of the UE; and after the adding the target PCell as an SCell: performing, by the UE, the PCell change, wherein the PCell change comprises: changing the target PCell to the PCell of the UE and changing the source PCell to the SCell that is in the active state and that is of the UE. receiving , by user equipment, UE, from a first base station, a message used for indicating a primary cell, PCell, change, wherein the first base station is a base station that a source PCell of the UE belongs to, and the message used for indicating a PCell change carries information about a target PCell; performing , by the UE, a PCell change based on the received message used for indicating a PCell change, wherein the PCell change comprises: changing the target PCell to a PCell of the UE and changing the source PCell to a secondary cell, SCell, that is in an active state and that is of the UE, and during the PCell change, the UE continues to perform data transmission with the source PCell and the target PCell; and sending, by the UE, a message used for indicating PCell change completion to the first base station or a second base station , wherein the second base station is a base station that the target PCell belongs to; wherein after the receiving a message used for indicating a PCell change, the PCell change further comprises: determining, by the UE, that the target PCell is not a serving cell of the UE; adding, by the UE, the target PCell as an SCell of the UE; and after the adding the target PCell as an SCell: determining, by the UE, that the target PCell is not a serving cell of the UE; adding, by the UE, the target PCell as an SCell of the UE; and after the adding the target PCell as an SCell: performing, by the UE, the PCell change, wherein the PCell change comprises: changing the target PCell to the PCell of the UE and changing the source PCell to the SCell that is in the active state and that is of the UE. <EOS>