A method for controlling transmission, comprising: determining, by a first radio access network device according to a service transmission condition of a terminal in a first single-mode wireless communications system, that a multimode wireless communications system comprising at least two wireless communications systems transmits a service for the terminal, wherein the at least two wireless communications systems are heterogeneous wireless communications systems, and wherein the first radio access network device is either a base station or a radio network controller, or a functional module in a base station or in a radio network controller; determining, by the first radio access network device, how many wireless communications systems are included in the multimode wireless communications system and which wireless communications systems are included in the multimode wireless communications system according to data volume of the service of the terminal, link quality of each wireless communications system included in the multimode wireless communications system, a type and capability of a service that can be carried by each wireless communications system included in the multimode wireless communications system and a cache idle rate of each wireless communications system included in the multimode wireless communications system; and sending, by the first radio access network device, first control information comprising link information of the at least two wireless communications systems to the terminal for switching a service, which is transmitted in the first single-mode wireless communications system, to the multimode wireless communications system according to the link information of the at least two wireless communications systems. determining, by a first radio access network device according to a service transmission condition of a terminal in a first single-mode wireless communications system, that a multimode wireless communications system comprising at least two wireless communications systems transmits a service for the terminal, wherein the at least two wireless communications systems are heterogeneous wireless communications systems, and wherein the first radio access network device is either a base station or a radio network controller, or a functional module in a base station or in a radio network controller; determining, by the first radio access network device, how many wireless communications systems are included in the multimode wireless communications system and which wireless communications systems are included in the multimode wireless communications system according to data volume of the service of the terminal, link quality of each wireless communications system included in the multimode wireless communications system, a type and capability of a service that can be carried by each wireless communications system included in the multimode wireless communications system and a cache idle rate of each wireless communications system included in the multimode wireless communications system; and sending, by the first radio access network device, first control information comprising link information of the at least two wireless communications systems to the terminal for switching a service, which is transmitted in the first single-mode wireless communications system, to the multimode wireless communications system according to the link information of the at least two wireless communications systems.