Abstract: A portable food radiation monitor has been developed and tested. This paper introduced the measurement structure, nuclear signal processing unit and the analysis application program. The nuclear signal processing unit includes anti-aliasing low-pass filter, programmable gain amplifier, high-speed A/D sampling, digital low-pass filter, trapezoidal shaping, pulse amplitude discrimination, and energy spectrum acquisition unit. The analysis application program includes functions for spectral line smooth, spectral peak-seeking, energy calibration, background deduction and activity calculation. The detection efficiency, the correction coefficient and the MDA of ¹³¹I have been determined. The calibration coefficient has been used to correct the radioactivity measurement results of 300 mL-food sample. The results show that the measurement error of monitor for ¹³¹I radioactivity in the general food is less than 10%, which satisfies the demand of food radioactive measurement.