It means: snake turns into dragon, and man becomes immortal. The achievement is extraordinary and unparalleled.
Dragon Palace: It is an undersea palace where the Dragon King lives in the myths and legends of the Han nationality.
Jiuzhong: that is, Jiuzhong Heaven. China tradition says that there are nine clouds in the sky (just ask the Taoist gods. Sanqing Shangsheng, Shenjiuchen) (Shen Xiao, Xiao Qing, Bixiao, Xiao Dan, Xiao Jing, Xiaoyu, Zhenxiao, Zixiao, Taixiao), "Jiuchongtian" is a quantifier, and the word Jiuchongtian means "limit" just because it is the largest number in the singular.