A method for controlling a multimode radio communications system, comprising: establishing, by a control server, a basic link between a terminal and any one communications system in the multimode radio communications system according to first settings; selecting, by the control server according to second settings, a communications system from the multimode radio communications system as a service communications system for transmission of each service of the terminal, wherein the second settings comprise signal quality of at least one other communications system in the multimode radio communications system than a current service communications system and the communications system that is corresponding to the basic link; and sending, by the control server, control information to the terminal on the basic link, wherein the control information is used to indicate the service communications system for transmission of each service of the terminal, wherein the basic link remains in an active state during transmission of services of the terminal; wherein before the selecting a communications system from the multimode radio communications system as a service communications system for transmission of each service of the terminal, the method further comprises: sending, by the control server, a second measurement indication to the terminal, wherein the second measurement indication is used as an indication of measuring signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link; and receiving, by the control server, the signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link, wherein the signal quality is reported by the terminal. establishing, by a control server, a basic link between a terminal and any one communications system in the multimode radio communications system according to first settings; selecting, by the control server according to second settings, a communications system from the multimode radio communications system as a service communications system for transmission of each service of the terminal, wherein the second settings comprise signal quality of at least one other communications system in the multimode radio communications system than a current service communications system and the communications system that is corresponding to the basic link; and sending, by the control server, control information to the terminal on the basic link, wherein the control information is used to indicate the service communications system for transmission of each service of the terminal, wherein the basic link remains in an active state during transmission of services of the terminal; wherein before the selecting a communications system from the multimode radio communications system as a service communications system for transmission of each service of the terminal, the method further comprises: sending, by the control server, a second measurement indication to the terminal, wherein the second measurement indication is used as an indication of measuring signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link; and receiving, by the control server, the signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link, wherein the signal quality is reported by the terminal. sending, by the control server, a second measurement indication to the terminal, wherein the second measurement indication is used as an indication of measuring signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link; and receiving, by the control server, the signal quality of the at least one other communications system in the multimode radio communications system than the current service communications system and the communications system that is corresponding to the basic link, wherein the signal quality is reported by the terminal.