The tradition of regarding the mountain forest as a recluse space can be traced back to “Summoning Recluse” in the Chu Ci and “Ingrained Opinions”, “The Way of Heaven” in the Zhuang zi, while the “mountain living poetry” is a specific kind of poetry developed by the Taoist priests and Buddhist monks who were seeking the Tao in reclusive lives. Most of the mountain living poems written by monk-poets and poets of the secular world during the Six Dynasties were aimed at searching for Buddhist or Taoist Tao. After Xie Lingyun completed his “Mountain Living Rhapsody”, the “mountain living tradition” of Confucianism, Taoism, and Buddhism established by monks and people of the secular world since the Late Han has finally found its expression in the synthesis of the Three Teachings. After the Tang dynasty was founded, the mountain living poetry became an important poetic genre. There are more than 150 poems with a title of “in the mountain”, “mountain living”, or “entering the mountain” in the Quantangshi. In this article, generally collected 48 of Kukai’s poetry works, 9 among these poems, which are one fifth of all, are written in the main tone of mountain living. They are apparently comparable with the mountain living poetry from the Six Dynasties to Early Tang and High Tang. This article has observed that although Kukai’s mountain living poems have contacted the synthesis of the Three Teachings in their thought contents, they are mainly going into the dharma gateway of Mahavairocana. These poems represent a practicing method which regards mountain as the “pure land” and keeps staying away from the filthy mundaneness. The sanctified mountain concept of Esoteric Buddhism, which is greatly different from Chinese mountain living poems from the Six Dynasties to Tang, states that to enter the mountain is to enter the dharmakaya of Buddha. Kukai’s mountain living poems display the using of “cloud” and “house” as imageries, which is similar to the ones written by Chinese monks. However, they are different in the contents that are denoted by imageries. From the aspect of the representational function of poetry, both Kukai’s and Chinese mountain living poems has the tendencies of “ego lyricizing” and “intercourse dialogue”, but Chinese living mountain poets are quiet reserved while Kukai’s works are vociferously discussing the Buddhist teaching.