The present invention provides a method for identifying a 3-D event location of a gamma interaction for enhancing the precision of event location determination and improving the practicability of an edge-on ends-read imaging detector. The method establishes two expected photopeak relations and a mapping table for every unit in the sensor array before imaging. In real practice, two sensing values with respect to the energy of scintillation photons generated during the detection on an event are obtained by the edge-on ends-read imaging detector. Furthermore, two energy windows corresponding to each sensing value are determined according to the corresponding expected photopeak relations. If both the two sensing values fall within the corresponding energy windows respectively, the event location along the long axis of sensor array is determined according to the sensor values with respect to the mapping table mentioned above.