The invention provides a multiplex fluorescent quantitative PCR primer and a probe for detecting H5, H7 and H9 subtype avian influenza viruses. With adoption of the primer and the probe, multiplex fluorescent quantitative PCR can be adopted to simultaneously detect which subtypes the H5, H7 and H9 subtype avian influenza viruses concretely are, no influences exist among the primers of different subtypes, the specificity is strong, the detection sensitivity is 10-50 copy numbers, a target sequence can be accurately detected quantitatively and qualitatively, the repeatability is good, and the reliability is high. The invention provides a multiplex fluorescent quantitative PCR kit for simultaneously detecting the H5, H7 and H9 subtype avian influenza viruses. The kit has the detection sensitivity being 10-50 copy numbers and is high in sensitivity and strong in specificity. The invention also provides a detection method which is good in stability. With adoption of plasmids with gene fusion as a positive standard substance, tedious operation of changing the positive standard substance for multiple times is avoided, the detection time is greatly shortened, the detection times are greatly reduced, and detection of a sample can be finished within 2h.