What clothes is Naxi's old man wearing behind his back?

It's a sheepskin shawl of Naxi nationality.

The sheepskin shawl of Naxi nationality has a history. According to myths and legends handed down, Naxi girls make exquisite sheepskin shawls based on Ying Gu's coat. This sheepskin shawl symbolizes hard work and courage, passed down from generation to generation and passed down to this day. Moreover, the sheepskin shawl contains the meaning of "Dai Yue Dai Xing", which means the diligence and hard work of Naxi people. Dai Yue, a Naxi woman wearing stars, is famous for her diligence, virtue and kindness. The traditional costumes of Naxi women have very distinctive national characteristics and formed their own unique style. The traditional culture of Naxi nationality contains rich historical and ideological connotations of Naxi nationality.