Objective To study the influence on STR typing for low copy number(LCN)DNA using different methods of amplifcation and detection.Methods Control DNA 9947A was diluted and then amplifled with Identifiler~(TM) or DNATyper15~(TM).The heat cycles were set to 28 or 28 add 6.Each template wag amplified three times in parallel,and then the amplified products or the product mixture of three amplifictions were deteced with 310 or 3130 Genetic Analyzer.Results The success rate of STR typing with the method 28+6 cycles was higher than that of 28 cycles.There are no correlation between the allele imbalance or allele dropout and STR locus.With the reduction in the amount of template DNA,allele imbalance and dropout gradually increased,and the allele dropout was more common than allele imbalance when the amount of template DNA Wag very small.When the product mixture of three amplifictions were deteced.the occurrence of allele imbalance and dropout reduce obviously.Conclusion The success rate of STR typing of LCN DNA can be obviously increased by detecting the product mixture of three amplifictions in parallel combined with the 28+6 heat cycle condition.