Abstract: A rapid radioactive inspection system was designed to measure the low-level radioactivity in the food. The double-fitting method was proposed to analyze the characteristic peak of measured spectrum. The curve fitting was taken to get the initial parameters, and then the boundary of characteristic peak could be determined by the interval range from i_c-5σ to i_c+5σ. The second curve fitting was taken to automatically obtain the net area of characteristic peak, and the quantitative analysis of rapid radioactive inspection system could be completed. At last, the double-fitting method was used to measure, compute and analyze the standard sample of ¹³⁷Cs. Based on these data, critical limit, detection limit and determination limit were calculated with different collecting time intervals and measurement relative standard errors. When the inspection time interval is 20 min, the detection limit of system is 8 Bq/L. If the relative standard error is 15%, the determination limit is about 16 Bq/L. The double-fitting method can be applied to the data processing of rapid radioactive inspection system, and can be used for qualitative and quantitative analysis of the low-level radioactivity.