A method for transmitting a signal, comprising: receiving, by a terminal device, a signal sent by a network device by using a plurality of downlink transmission beam groups; and sending, by the terminal device, first information to the network device, so that the network device determines a first downlink transmission beam group from the plurality of downlink transmission beam groups, at least one of the plurality of downlink transmission beam groups comprising a plurality of downlink transmission beams, wherein, after sending, by the terminal device, the first information to the network device, the method further comprises: sending, by the terminal device, second information to the network device, so that the network device determines a first downlink transmission beam from the plurality of downlink transmission beam groups, the first downlink transmission beam being a downlink transmission beam that is expected by the terminal device for the network device to transmit a subsequent signal, wherein, before sending, by the terminal device, the second information to the network device, the method further comprises: receiving, by the terminal device, third information sent by the network device, the third information being used to indicate whether the terminal device needs to send the second information to the network device; and determining, by the terminal device, whether to send the second information to the network device according to the third information. receiving, by a terminal device, a signal sent by a network device by using a plurality of downlink transmission beam groups; and sending, by the terminal device, first information to the network device, so that the network device determines a first downlink transmission beam group from the plurality of downlink transmission beam groups, at least one of the plurality of downlink transmission beam groups comprising a plurality of downlink transmission beams, wherein, after sending, by the terminal device, the first information to the network device, the method further comprises: sending, by the terminal device, second information to the network device, so that the network device determines a first downlink transmission beam from the plurality of downlink transmission beam groups, the first downlink transmission beam being a downlink transmission beam that is expected by the terminal device for the network device to transmit a subsequent signal, wherein, before sending, by the terminal device, the second information to the network device, the method further comprises: receiving, by the terminal device, third information sent by the network device, the third information being used to indicate whether the terminal device needs to send the second information to the network device; and determining, by the terminal device, whether to send the second information to the network device according to the third information. sending, by the terminal device, second information to the network device, so that the network device determines a first downlink transmission beam from the plurality of downlink transmission beam groups, the first downlink transmission beam being a downlink transmission beam that is expected by the terminal device for the network device to transmit a subsequent signal, wherein, before sending, by the terminal device, the second information to the network device, the method further comprises: receiving, by the terminal device, third information sent by the network device, the third information being used to indicate whether the terminal device needs to send the second information to the network device; and determining, by the terminal device, whether to send the second information to the network device according to the third information. receiving, by the terminal device, third information sent by the network device, the third information being used to indicate whether the terminal device needs to send the second information to the network device; and determining, by the terminal device, whether to send the second information to the network device according to the third information.