Embodiments of the present invention provide a method for controlling a multimode radio communications system, a control server, and a terminal. The method includes: establishing, by the control server, a basic link between the 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; and sending, by the control server, control information to the terminal on the basic link, where the control information is used to indicate the service communications system for transmission of each service of the terminal. The embodiments of the present invention improve a utilization rate of radio resources and user experience in a multimode radio communications environment.