The invention discloses an F9 gene copy number variation detection kit which comprises a 2*PCR (Polymerase China Reaction) buffer solution, competitive DNA, PCR primer mixed liquor and Taq DNA polymerase. An AccuCopy technology has high precision, variable coefficient of being less than 5% and high result accuracy. Therefore, according to the F9 gene copy number variation detection kit developed by the AccuCopy technology, about 15 patients suffering hemophilia B with large deletion mutation is detected and found, and the clinical application effect is good.