Why is Song of Eternal Sorrow a poetic novel?

This statement is not entirely correct. "Poetic novel" is a western concept, focusing on poetic novel, which is a novel with poetic aesthetics rather than a poem with novel elements. It can be called novel poetry. Of course, this is just a personal understanding.

From the full text, The Song of Eternal Sorrow can be divided into three sections. The first section, from "the emperor of China, who lusted after the beauty of an empire for many years, searched and never found it" to "until the war drum, from Yuyang boom, shook the earth and broke the tune of the rainbow skirt and feather coat". : tells the story of Yuhuan entering the palace as a pet. The second paragraph reads "The Forbidden City, a nine-story palace, vaguely in the dust, from thousands of horses and chariots to the southwest." Year after year, the distance between life and death, but not a beloved soul visited his dream. The third paragraph, from "there lived a Taoist priest in Lingqiong, who was a heavenly guest and could summon the gods attentively" to the end, tells the story of the Tang Dynasty emperor's pursuit of beauty. The paragraphs are clearly drawn, and the main line is the story of Emperor Xuanzong of Tang Dynasty and Yang Guifei.