Abstract: Through the research of unconformity between Tousuquan formation in middle Devonian Period and Dananhu formation in early Devonian Period,We think that the sedimentary environment of Dananhu formation was island arc of sea facies and that of Tousuquan was continental facies.Unconformity between them meants an epeirogenic movement, so we established it "Big marsh movement" This movement made the earth crust risen and the north Tianshan ocean close. At last,evolution history of north Tianshan ocean was over.