Highly pathogenic avian influenza (HPAI) is a persistent threat to poultry, wild birds, humans, and other mammals. The continually evolving HPAI H5N6 virus has induced great losses in breeding industries in growing regions around the world. In this study, we confirmed an outbreak of the HPAI H5N6 virus in captive Pavo cristatus in Jiangxi Province, China. The causative agents H5N6 viruses were isolated and designated JS01, JS02, and K10. Animal experiments showed that all three isolates exhibited high pathogenicity to chickens, but they need adaption to effectively infect mice. A phylogenetic analysis showed that all three isolates were clustered in H5 clade 2.3.4.4c. No novel genetic reassortant was found in JS01, JS02, and K10 viruses. It was estimated that JS01, JS02, and K10 H5N6 viruses were direct descendants of the H5N6 virus circulating in South of China. The estimated divergence time from tMRCAs was anywhere between May 2014 to June 2016. Although the number of outbreaks of avian influenza decreased significantly in 2018, the threat from avian influenza to public health remains serious. Enhanced active surveillance is required to monitor the transmission and evolution of H5 influenza viruses.