Abstract: To solve the problem of direct ¹³¹I activity measurement in human thyroid for radiological protection and diagnosis and treatment in nuclear medicine, and the problem of traceability of related instruments for ¹³¹I activity measurement in human thyroid, a portable on-site radioactivity measurement metrological standard device was developed. In combination with the IAEA/ANSI neck phantom, the detection efficiency calibration and activity determination methods of the standardization were studied. Through experimental measurement and simulation calculation, the efficiency curve at different detection distances was determined, and the traceability method of ¹³¹I activity in the human thyroid was established. The minimum detectable activity reached 4.67 Bq when the standard was directly measured close to the neck for 600s; the portable gamma spectrometer used to measure the activity of ¹³¹I in the human thyroid was calibrated with the relative expanded uncertainty of 5.5% (k=2). The development of this standard has established a key equipment foundation for the accurate measurement and traceability of ¹³¹I activity in occupational health monitoring, nuclear emergency, and diagnosis and treatment of thyroid diseases.