Research on Chinese Poetic theory could be divided into two approaches. The first approach aimed at poem itself, including topic meaning, formation skill, art character and style. The second approach aimed to elucidate or deduce poetics, including checking poetic theory, analyzing special jargons, exploring origins and development of poets and creating writing theory etc. In the researches of plural and abundant poetics or fable fields, "fable poem" have been ignored in a long time. Forgotten fable poem, hided in every corner of poems. For example, in the mid-Tang dynasty, Liu Yu Xi owned ten more poems, Yuan Zhen owned twenty more poems, Bai Ju Yi owned fifty more poems. The three poets owned one hundred more poems totally. Let alone another poet. So fable poem should be more abundant than we had known, especially in the mid-Tang dynasty. Bai Ju Yi's fable poem almost could be treated as a new sub-literature field. Not only Bai Ju Yi created a lot of chanting poems, but also wrote fable poems. Thus, discovery of fable poem will be a new accessible approach. The paper based on these assumptions. I rethink that what's the definition of fable poem? What's its nature? What's the relationship compared to the other sub-literature? Because fable poem included two parts: "fable ontology" and "real ontology". "Fable ontology" is so called story or content, and "real ontology" is so called meanings of fable. So fable poem would be overlapped with descriptive poem when presenting story or content. When fable poem revealed its meaning, it would be overlapped with chanting object poem. Both of them all owned double meaning behind poem itself. Besides, is there state of overlapping between writing fable poem and traditional skill, such as Fu Bi Xing? According to this, the paper aimed to elucidate the definition and category of fable poem and to analyze the relationship between fable poem and the other sub-literature. I hope the character and style of fable poem would be more clearly presented.