Using a well type NaI(Tl)gamma spectrometer,the radioactivity of ~(125)I was measured with absolute measurement method.~(125)I radioactive source was prepared with the same batch of radioactive solution,and its activity range is 10~2-10~4 Bq.By different strength activity measurement Using a well type NaI (Tl) gamma spectrometer, the radioactivity of ~ (125) I was measured with an absolute measurement method. ~ (125) I was radioactive source was prepared with the same batch of radioactive solution, and its activity range is 10 ~ 2-10 ~ 4 Bq.By different strength activity measurement