An information transmission method, comprising: receiving, by a terminal device, a request message sent by a network device, wherein the request message carries information comprising a carrier aggregation band combination range, and the carrier aggregation band combination range comprises at least one of a requested band in which a carrier in a carrier aggregation band combination is located, a requested maximum bandwidth of carriers in the carrier aggregation band combination, and a requested maximum quantity of the carriers in the carrier aggregation band combination; determining, by the terminal device, a carrier aggregation capability and baseband capabilities of the terminal device, wherein the carrier aggregation capability comprises a quantity of carriers and a bandwidth of a carrier in the carrier aggregation band combination supported by the terminal device, and the baseband capabilities comprise a multiple-input multiple-output, MIMO, capability, wherein the MIMO capability is used to indicate a quantity of MIMO layers that is capable of being processed by the terminal device; sending, by the terminal device, information of the carrier aggregation capability and the baseband capabilities to the network device; and receiving, by the terminal device, configuration information, sent by the network device, wherein the configuration information comprises a target baseband capability information of the terminal device when the terminal device works on the carrier in the carrier aggregation combination, the determining a carrier aggregation capability and baseband capabilities of the terminal device comprises: determining the carrier aggregation capability, wherein the carrier aggregation capability meets the carrier aggregation band combination range, and the carrier aggregation capability comprises the carrier aggregation band combination; determining a baseband capability range based on the carrier aggregation capability; and determining the baseband capabilities, wherein the baseband capabilities meet the baseband capability range, and the baseband capabilities is with regard to each of at least one class of carrier information, and the carrier information comprises a quantity of carriers and a bandwidth of a carrier. receiving, by a terminal device, a request message sent by a network device, wherein the request message carries information comprising a carrier aggregation band combination range, and the carrier aggregation band combination range comprises at least one of a requested band in which a carrier in a carrier aggregation band combination is located, a requested maximum bandwidth of carriers in the carrier aggregation band combination, and a requested maximum quantity of the carriers in the carrier aggregation band combination; determining, by the terminal device, a carrier aggregation capability and baseband capabilities of the terminal device, wherein the carrier aggregation capability comprises a quantity of carriers and a bandwidth of a carrier in the carrier aggregation band combination supported by the terminal device, and the baseband capabilities comprise a multiple-input multiple-output, MIMO, capability, wherein the MIMO capability is used to indicate a quantity of MIMO layers that is capable of being processed by the terminal device; sending, by the terminal device, information of the carrier aggregation capability and the baseband capabilities to the network device; and receiving, by the terminal device, configuration information, sent by the network device, wherein the configuration information comprises a target baseband capability information of the terminal device when the terminal device works on the carrier in the carrier aggregation combination, the determining a carrier aggregation capability and baseband capabilities of the terminal device comprises: determining the carrier aggregation capability, wherein the carrier aggregation capability meets the carrier aggregation band combination range, and the carrier aggregation capability comprises the carrier aggregation band combination; determining a baseband capability range based on the carrier aggregation capability; and determining the baseband capabilities, wherein the baseband capabilities meet the baseband capability range, and the baseband capabilities is with regard to each of at least one class of carrier information, and the carrier information comprises a quantity of carriers and a bandwidth of a carrier. determining the carrier aggregation capability, wherein the carrier aggregation capability meets the carrier aggregation band combination range, and the carrier aggregation capability comprises the carrier aggregation band combination; determining a baseband capability range based on the carrier aggregation capability; and determining the baseband capabilities, wherein the baseband capabilities meet the baseband capability range, and the baseband capabilities is with regard to each of at least one class of carrier information, and the carrier information comprises a quantity of carriers and a bandwidth of a carrier.