In order to improve the experimental and creative ability of the senior under grade students，and arouse their interest and enthusiasm in the physical experiments，a new research experiment，named “energy resolution of the CsI( Tl) scintillator detectors”is set up. The students should package and install the CsI ( Tl) detectors by themselves，build their own testing platform and then measure the energy resolution of CsI ( Tl) scintillator detectors made by themselves. This experiment provides many opportunities for the students to participate in and hands-on. It is found that this research experiment is suitable for the senior under - grade students via the teaching practice of three years from 2013 to 2015.