Abstract: Objective To introduce real-time polymerase chain reaction （real-time PCR） into the initial sample screening, to improve the effectiveness of traditional trace sample extraction method. Methods Serial diluted 9947A was quantified using a Rotor-Gene Q real-time RT-PCR, and the genotype was determined with AmpF?STRTM IdentifilerTM Plus PCR kit. Thus a quantitative threshold model was built to obtain complete STR typing from the trace samples. In addition, 903 trace samples were used to verify the reliability. Results When the samples quality concentration was >0.03 ng/μL, the effective STR typing could be directly obtained; when the concentration was >0.01 and ≤0.03 ng/μL, the effective STR typing could be directly obtained by optimizing the PCR thermal cycle parameters （30 cycles）; and when the concentration was ≤0.01 ng/μL, no effective map could be obtained even if PCR was optimized. Conclusion The real-time PCR quantitative threshold model is effective for the screening of trace samples.forensic genetics; tandem repeat

Key words: forensic genetics, tandem repeat sequences, real-time fluorescence quantification, trace samples