The present invention relates to a stabilization method of a plastic scintillator-based radiation detector of the present invention, wherein the Compton edge of K-40 that exists in the spectrum of a background radiation that reacts with the plastic scintillator is converted into a peak form through a proper signal process, and the output calibration of the detector is automatically performed in real time by using the information. Thus, the output of the plastic scintillator-based radiation detector is automatically calibrated in order to thereby stabilize the output of the detector regardless of the external environmental changes.