Abstract: With the wide spread applications of radioactive sources and radiation devices, the probability of radiation accidents caused by sources becomes larger. Therefore, how to locate and safely find those radioactive sources, which had been lost is quite important. In this paper, a triangular cylindrical lead shield NaI detector was designed to locate the radioactive source. In the experiment, the influences of the measuring time, the thickness of the lead shield, the distance between the radioactive source and the detector, and the energy of the gamma ray on the location accuracy of the radioactive source were studied. The experimental results show that for ¹³⁷Cs source, when the air absorbed dose rate is ≥0.028 μGy/h, the average angle deviation from air sorption is ≤1.24°. For ⁶⁰Co source, when the air absorbed dose rate is 0.4 μGy/h, the average angle measurement deviation is 1.16°. For 9.25×10⁵ Bq ¹³⁷Cs source, position deviation within the distance of 1.5 m is about 0.097 m.