Abstract: The portable γ spectrometer can be used for identification of typical nuclides in the primary coolant and acquiring their activity concentrations in situ. The source-peak efficiency should be calibrated to ascertain the relationship between the net area under the characteristic peak of typical nuclide and its genuine activity concentration in the water sample. The efficiency calibration curve was acquired by measuring the mixed solution of ¹³³Ba, ¹³⁷Cs and ⁶⁰Co nuclides, and then ¹³⁷Cs standard liquid and simulated ¹³¹I standard liquid were measured respectively. Test results indicate that the spectrometer can identify typical nuclides ¹³⁷Cs and ¹³¹I, and the measuring relative error of activity concentration is less than 10%, which satisfies the requirement of measurement accuracy and sensitivity for fuel element rupture detection.