This study focuses on the image of poetic origin and co-occurrence relation of onomatopoeia “Xiaoxiao(蕭蕭)”. “Xiao(蕭)” originally indicated “Artemisia”. But, in the form of “Xiaoxiao(蕭蕭)”, it is used as an onomatopoeia indicating the cry of horse, sound of wind or sound of falling leaves. The poetic origin of “Xiaoxiao(蕭蕭)” as an onomatopoeia can be found in the expressions ≪Shijing (詩經)≫, ≪Chuci(楚辭)≫, and < Yishuige(易水歌) > which form the co-occurrence relation with the cry of horse, or the sound of wind, rain or falling leaves. Then, in the subsequent poems, the image of “Xiaoxiao(蕭蕭)” became accepted or modified. As such, the onomatopoeia has been widely used in the poem because its auditory element in the reiterative was proper for maximizing the rhythm and image of poem. Though the cry of horse which has the co-occurrence relation with “Xiaoxiao(蕭蕭)” expressed the meaning of “not noisy” as shown in the example of ≪Shijing(詩經)≫, it formed a new image of “being sad” in combination with the images such as separation or war in subsequent period. In addition, the “Xiaoxiao(蕭蕭)” also got the image of ”being lonely” as the sound of wind, rain or falling leaves combined with the emotion of the “sad fall”. As such, the sad emotion and image in Chinese classical poetry have been condensed in the onomatopoeia “Xiaoxiao(蕭蕭)” and passed down to this day. The word “Xiaoxiao(蕭蕭)” has affected the classical poetry in Korea and Japan and has been widely accepted as the poetic words expressing the emotion and image of fall.