Embodiments of the present disclosure provide a multi-connectivity communication method and a device. An access network device of a first network determines to use an access network device of a second network to perform data splitting for data of UE, and then sends first splitting configuration information to the UE and sends second splitting configuration information to the access network device of the second network. The first splitting configuration information is used to notify the UE that the access network device of the second network is to split to-be-split data of the UE. The second splitting configuration information is used to instruct the access network device of the second network to split the to-be-split data of the UE.