A method for transmitting a signal and a communications apparatus are provided. The method includes: obtaining a signal transmission mode, where the signal transmission mode indicates that an uplink signal is transmitted in a multiplexing mode; and transmitting the uplink signal on an uplink band and a downlink band in the multiplexing mode according to the obtained signal transmission mode. The communications apparatus includes: a first obtaining unit, configured to obtain a signal transmission mode, where the signal transmission mode indicates that an uplink signals is transmitted in a multiplexing mode; and a transmitting unit, configured to transmit the uplink signal on an uplink band and a downlink band in the multiplexing mode according to the obtained signal transmission mode. The technical solutions of embodiments of the present invention can reduce signaling overheads of the system and improve spectrum efficiency of the system when obtaining channel state information (CSI).