Based on an analysis of sedimentary sequence, regional unconformity, lithologic character and distribution of Paleogene-Neogene sediments, the authors hold that the Paleogene-Neogene sediments can be divided into four upward-shallowing sequences of Tuotuohe Formation, Yaxicuo Formation, Wudaoliang Formation and Quguo Formation, which constitute two complete continental orogenic molasses formation sequences. Basin analysis shows that the Paleogene-Neogene Tuotuohe basin has experienced such evolutionary stages as foreland basin evolution stage (56.5～45.0 Ma)→strike-slip pull-apart basin stage(45.0～30.0 Ma)→overall uplift and intermountain residual basin stage (23.5～16.0 Ma)→foreland basin-confined basin-intermountain residual basin stage (16～2.6？ Ma). According to tectonic, lithofacies and paleographic evolution, it is considered that at the early stage of the deposition of Yaxicuo Formation (45 Ma or so), regional geotectonic background experienced remarkable transformation from the regional compression-thickening stage to the domination of inter-plate lateral strike-slip action, thus entering into the intracontinental plate convergence evolution stage. Viewed from Paleogene-Neogene sedimentary evolution of the Tuotuohe basin, the collision between the Indian plate and the Eurasian plate was of pulsation nature, the four regional surfaces of unconformity and two molasses formation seq uences in the whole Paleogene-Neogene sedimentation seemed to be sedimentary response to pulsating orogenic process, and the initial collision probably took place at the time when Cretaceous changed into Paleogene before 56.5 Ma.