A signal processing method and a related device, where the signal processing method may be applicable to the field of signal transmission between a baseband processing apparatus and a radio frequency apparatus of an access network device. The baseband processing apparatus obtains at least two first downlink digital baseband signals, multiplexes the at least two first downlink digital baseband signals into one second downlink digital baseband signal, and after converting the second downlink digital baseband signal into a first downlink analog baseband signal, sends the first downlink analog baseband signal to the radio frequency apparatus. The radio frequency apparatus demultiplexes the first downlink analog baseband signal, and generates, based on at least two second downlink analog baseband signals obtained by demultiplexing, a downlink radio frequency signal to be sent to a terminal device.