The present application discloses a method and an apparatus for transmitting downlink data, to resolve the issue of erroneous transmission of downlink data of UE when the UE moves from an EPS network to a 5G network. The method comprises: after receiving a request message for updating a session management context of the UE, a session management function entity in embodiments of the present application determining that the UE has moved from a first network to a second network; the session management function entity notifying a user plane function entity to delete a user plane connection of the UE in the first network, and creating a user plane connection of the UE in the second network, such that the user plane function entity transmits downlink data of the UE through the newly created user plane connection.