The present disclosure provides an apparatus for processing signals for a plurality of energy regions, and a system and method for detecting radiation of a plurality of energy regions. The apparatus for processing signals for a plurality of energy regions may comprise: a first processor, configured to receive a signal from a detector and process the received signal to generate a gated signal, wherein a turn-on period of the gated signal represents magnitude of the received signal; and a second processor, configured to receive the gated signal from the first processor, and determine one of the plurality of energy regions to which the received signal belongs according to the turn-on period of the gated signal, so as to count signals within the determined energy region.