A radiation detection signal processing method and a radiation detection signal processing system using the method are provided, which combine trigger signals and time mark information. The method includes: providing a radiation detection signal processing system having a plurality of front-end detectors, where each front-end detector detects a radiation event to generate a corresponding energy signal; generating a corresponding trigger signal according to the corresponding energy signal; generating a first signal and a second signal according to all trigger signals; and obtaining time differences among the trigger signals according to the first signal and the second signal, converting the time differences into a set of time marks, merging all of the trigger signals and the set of time marks into a hybrid time signal, and transmitting the hybrid time signal to a hybrid event coincidence detection circuit.