The Ailaoshan suture (ALSS) is one of the important Paleo-Tethyan sutures in Southeast Asia, and the Late Paleozoic basic rocks in the ALSS are the key to reconstructing the Paleo-Tethyan evolution. However, the petrogenesis and tectonic environments of these basic rocks are controversial, and this controversy constrains researchers' understanding of the Paleo-Tetyan evolution. Based on field investigation, the authors studied petrological and geochemical characteristics and synthesized the geochronological and geochemical data of the Late Paleozoic basic rocks in the western part of the ALSS, with the purpose of investigating their petrogenesis and tectonic setting and further providing insights into the ALSS evolution. Zircon U-Pb data suggest that the Wusu and Baliu basic rocks were formed in Early-Permian (288~287 Ma), and Dalongkai and Yaxuanqiao basic rocks were formed in Mid-Permian (272~265 Ma). The products of Early-Permian magmatism are calc-alkaline in composition, and they have island-arc basalt (IAB)-like geochemical features with high rare earth element (REE) content (ΣREE=59.75×10^-6~135.08×10^-6), LREE/HREE ratios (2.64~3.32), Ta/Yb (0.09~0.18) and Ce/Yb (6.59~9.03) ratios, and slight enrichment in large ion lithophile elements (LILEs, e.g., Rb, Ba and Th) and depletion in high field strength elements (HFSEs, e.g., Nb, Ta and Ti), whereas the basic rocks from Mid-Permian magmatism are tholeiite, and are characterized by low REE content (ΣREE=28.77×10^-6~76.16×10^-6), LREE/HREE ratios (1.75~2.55), Ta/Yb (0.05~0.09) and Ce/Yb (3.58~5.97) ratios, and strong enrichment in LILEs and depletion in HFSEs. Combined with regional geological data, this paper proposes a two-pulse model related to the Late Paleozoic subduction in the western part of ALSS. During the Early-Permian, the westward subduction of the Ailaoshan branch ocean/back-arc basin beneath the east margin of Simao terrane induced partial melting of mantle wedge to form the Andean-type continental margin arc along the western Ailaoshan; subsequently (Mid-Permian), the collapse of continental margin arc formed a back-arc basin, and further produced basic-ultra basic rocks with the geochemical features of both MORB and volcanic arcs.