The 50s-60s in the 20 th century is usually considered as a transitional period in the history of American poetry. Before the mid-50 s, Eliot and his follower—the American New Criticism took the dominant position in the field of American poetry and literary criticism. After the mid-50 s, postmodernist poetry, represented by William Carlos Williams, Allen Ginsberg and Robert Lowell,gradually came onto the historical stage. Based on the social and historical background, the article tries to figure out the representative figures and important events in the period, and presents a clear picture of transition in the modern American poetry.