Abstract: The Quaternary debris flow deposits were discovered for the first time on the western slope of the Longquan Mountains in western Sichuan. The sedimentary facies associations AA1B, AA1C and AA1 suggest that the debris flow deposits were accumulated in the central part of the alluvial fan, and represented by the viscous debris flow deposits. The ESR age dating and sporopollen assemblages show that the debris flow deposits were deposited under the warm and humid climatic conditions during the early-middle Pleistocene. The formation of the debris flow deposits has reflected the tectonic uplift of the Longquan Mountains at the early-middle Pleistocene boundary and breakup of the level surface in the Sichuan Basin, and may be the response to the Qinghai-Xizang Plateau uplift, strong monsoon and storm precipitation. The findings in this study may have important implications for better understanding of the Quaternary tectonism and palaeoclimates in the Sichuan Basin and eastern margin of the Qinghai-Xizang Plateau.