Two ductile deformations were identified in Beidashan area, which lies in the western Alxa Block. Early ductile deformation is characterized by top-to-the-north (northwest) ductile thrust structure, and a late Silurian metamorphic age of 422±1 Ma was yielded by the paragneiss which was related to the thrust deformation. Later ductile deformation was characterized by EW-trending sinistral shear, and two zircon U-Pb crystallization ages of 326.2±1.2 Ma and 323.8±2.6 Ma were yielded for two monzonitic granites which experienced the shear deformation. Combined with previous research on Alxa Block, a comprehensive comparison of the late Ordovician-Carboniferous magmatic-metamorphic-deformation events between the western and the eastern Alxa Block was made in this study. On the one hand, the characteristics and ages of two ductile deformations in Beidashan are similar to those of Bayanwulashan-Langshan which lies in the eastern Alxa Block. On the other hand, late Ordovician-Carboniferous magmatic rocks in the western and eastern Alxa Block also have similar rock types, ages as well as geochemical and Nd isotopic characteristics. All these characteristics indicate that the western and eastern Alxa Block went through the same tectonic evolution, and these authors also hold that a late Ordovician-Carboniferous tectonic-magmatic belt was developed in the early Precambrian metamorphic basement of the Alxa Block. This tectonic-magmatic belt extends from the Taohualashan in the west, through Beidashan, Nuoergong, Bayanwulashan, to the Langshan in the east and its origin was related to the continuous southward subduction of the Paleo Asian Ocean.