A radio frequency front end for applying carrier aggregation to a terminal device, comprising: P transmit branches, wherein each transmit branch is used to transmit a carrier modulation signal on at least one of M different frequency bands, each transmit branch comprises at least one transmit filter, the transmit filter is a band-pass filter, a frequency band on which a carrier is allowed by the transmit filter to pass is consistent with the at least one frequency band on which transmitting is performed on each transmit branch, P is an integer greater than or equal to 1 and less than or equal to M, and M is an integer greater than or equal to 2; N receive branches, wherein each receive branch is used to receive a carrier modulation signal on at least one of the M different frequency bands, each receive branch comprises at least one receive filter, the receive filter is a band-pass filter, and a frequency band on which a carrier is allowed by the receive filter to pass is consistent with the at least one frequency band on which receiving is performed on each receive branch, and N is an integer greater than or equal to 1 and less than or equal to M; and a switch circuit having L input ports and at least one output port, wherein the output port is connected to an antenna or a back end circuit of an antenna, the L input ports are used to simultaneously connect a transmit branch of the P transmit branches and a receive branch of the N receive branches, wherein the transmit branch and the receive branch are corresponding to a same frequency band, and L is an integer greater than or equal to 2; wherein each transmit branch further comprises an isolator, wherein the isolator is disposed between the transmit filter and the switch circuit; and the isolator is used to reduce mutual impact between the transmit filter and another transmit filter or the receive filter; and wherein: in downlink carrier aggregation for at least two frequency bands, the L input ports simultaneously connect receive branches corresponding to the at least two frequency bands and a transmit branch corresponding to one of the at least two frequency bands; and in uplink carrier aggregation for the at least two frequency bands, the L input ports simultaneously connect transmit branches corresponding to the at least two frequency bands and a receive branch corresponding to one of the at least two frequency bands. P transmit branches, wherein each transmit branch is used to transmit a carrier modulation signal on at least one of M different frequency bands, each transmit branch comprises at least one transmit filter, the transmit filter is a band-pass filter, a frequency band on which a carrier is allowed by the transmit filter to pass is consistent with the at least one frequency band on which transmitting is performed on each transmit branch, P is an integer greater than or equal to 1 and less than or equal to M, and M is an integer greater than or equal to 2; N receive branches, wherein each receive branch is used to receive a carrier modulation signal on at least one of the M different frequency bands, each receive branch comprises at least one receive filter, the receive filter is a band-pass filter, and a frequency band on which a carrier is allowed by the receive filter to pass is consistent with the at least one frequency band on which receiving is performed on each receive branch, and N is an integer greater than or equal to 1 and less than or equal to M; and a switch circuit having L input ports and at least one output port, wherein the output port is connected to an antenna or a back end circuit of an antenna, the L input ports are used to simultaneously connect a transmit branch of the P transmit branches and a receive branch of the N receive branches, wherein the transmit branch and the receive branch are corresponding to a same frequency band, and L is an integer greater than or equal to 2; wherein each transmit branch further comprises an isolator, wherein the isolator is disposed between the transmit filter and the switch circuit; and the isolator is used to reduce mutual impact between the transmit filter and another transmit filter or the receive filter; and wherein: in downlink carrier aggregation for at least two frequency bands, the L input ports simultaneously connect receive branches corresponding to the at least two frequency bands and a transmit branch corresponding to one of the at least two frequency bands; and in uplink carrier aggregation for the at least two frequency bands, the L input ports simultaneously connect transmit branches corresponding to the at least two frequency bands and a receive branch corresponding to one of the at least two frequency bands. in downlink carrier aggregation for at least two frequency bands, the L input ports simultaneously connect receive branches corresponding to the at least two frequency bands and a transmit branch corresponding to one of the at least two frequency bands; and in uplink carrier aggregation for the at least two frequency bands, the L input ports simultaneously connect transmit branches corresponding to the at least two frequency bands and a receive branch corresponding to one of the at least two frequency bands.