What's the difference between ancient, modern and modern poetry?

I guess you're asking about ancient poetry and modern poetry. Modern poetry refers to the poems that pay attention to flat and rhyming after the Tang Dynasty, including metrical quatrains, and others can be called ancient poetry.

1953 "Modern Poetry Society" was established under the name of "Modern Poetry" for the first time.

China's modern poetry can be divided into two relatively independent stages:

Poetry before the first half of the 20th century is called China's modern poetry.

Poetry after the second half of the 20th century is called China's contemporary poetry.

I guess so.