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; 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; the method characterized in that it further comprises the steps of: determining, by the control server, if any one downlink service of the terminal is transmitted in at least two service communications systems, a percentage of downlink service data of the terminal transmitted among the at least two service communications systems according to a load condition of the at least two service communications systems and/or link quality of the at least two service communications systems; and sending, by the control server, first offload information to the terminal on the basic link, wherein the first offload information is used to indicate the percentage of downlink service data of the terminal transmitted among the at least two service communications systems. 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; 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; the method characterized in that it further comprises the steps of: determining, by the control server, if any one downlink service of the terminal is transmitted in at least two service communications systems, a percentage of downlink service data of the terminal transmitted among the at least two service communications systems according to a load condition of the at least two service communications systems and/or link quality of the at least two service communications systems; and sending, by the control server, first offload information to the terminal on the basic link, wherein the first offload information is used to indicate the percentage of downlink service data of the terminal transmitted among the at least two service communications systems. determining, by the control server, if any one downlink service of the terminal is transmitted in at least two service communications systems, a percentage of downlink service data of the terminal transmitted among the at least two service communications systems according to a load condition of the at least two service communications systems and/or link quality of the at least two service communications systems; and sending, by the control server, first offload information to the terminal on the basic link, wherein the first offload information is used to indicate the percentage of downlink service data of the terminal transmitted among the at least two service communications systems.