In the field of signal processing technologies, a microwave transmission apparatus, a signal processing method and device in a microwave transmission apparatus are provided, which are capable of improving the signal-to-noise ratio of the service signal and the reliability of the communication signal, and increasing the distance between an indoor unit (IDU) and an outdoor unit (ODU). In the technical solutions, a signal processing method in a microwave transmission apparatus includes: directly multiplexing at least a service signal and a non-service signal, and converting the multiplexed electric signal into a multiplexed optical signal; and sending the multiplexed optical signal to an ODU.