This paper aims to evaluate the continuity and the discontinuity of American poetry toward 21st century in modern American poetry since 1990. In the evaluation of important modern American poetry since 1990, many reputable award programs, anthologies, critical reviews, and annual bibliographies are used; for example, Associated Writing Programs, A New American Poetry(1994), Yale Younger Poets Series, and The Best American Poetry. About 120 poets who actively publish poems since 1990 get serious attention from professional critics and the public. These poets can be divided into two groups: the progressive and the conservative. While the conservative poets stick to continuity of traditional American poetics, the progressive keep exploring new poetics. In particular, the progressive poets dominate the world of modern American poetry by breaking traditional ideas, methods, and forms. Unlike the traditional poets who follow romantic notion of typical American lyric poetry, the progressive poets deal with such new experimental themes and subject matters as "realityless reality" and cinematic poetry. Therefore, modern American poetry since 1990 becomes more theoretic and complex than ever. In the specific analysis, some representing poems of A. R. Ammons, John Ashbery, Adrienne Rich, Allen Ginsberg, Carolyn Forche, Gary Snyder, Kenneth Koch, David Ignatow, Denise Levertov, Donald Hall, Diane Wakoski, W. S. Merwin, Mark Strand, James Merrill, Maxine Kumin, Bob Perelman, and Robert Long are discussed to exemplify the continuity and the discontinuity of American poetics toward 21st century in modern American poetry since 1990. In conclusion, modern American poetry since 1990 is heading for the deeper sophisticated and organic conflicts between continuity and discontinuity, reality and imagination, self and others, human and God, sound and silence, art and life toward the 21st century.