Lying along the Solonker-Linxi collisional orogenic suture zone in Sonid Youqi of Inner Mongolia, the Chaganchulu A-type monzogranite intruded into the Early Permian Halengling SSZ type ophiolitic tectonic melange belt. Based on the systematic field geological characteristics, petrology, geochemistry, zircon U-Pb chronology, the purpose of this study is to determine the genetic type of pluton, tectonic setting, and provide evidence for the closing time of the ocean basin in the eastern part of the Paleo-Asian Ocean. LA-ICP-MS zircon U-Pb dating shows that the age of the granite is 245.9±1.3 Ma, indicating that the formation age is Middle Triassic. The granite contains more alkaline feldspars, and the dark mineral is mainly biotite, with cave structure. The granite is geochemically characterized by high SiO₂ (76.75%~77.18%) and alkali (Na₂O+K₂O=8.19%~8.62%), but low CaO (0.40%~0.44%) and MgO (0.03%~0.05%). The granite has obvious negative Eu anomaly (Eu=0.03~0.09), relative enrichment of Rb, Th, U, K and Ga, depletion of Ba, Sr, P and Ti, as well as high 10 000 Ga/Al (2.72~3.52), ^TFeO/MgO (29.16~57.82), (Na₂O+K₂O)/CaO (15.08~21.39). The petrological, mineralogical and geochemical characteristics of the granite show the characteristics of A-type granite. According to the regional, Mesozoic A-type granites have positive correlation εNd(t) value and young Nd age suggest that the granite may be caused by partial melting of intermediate basic crust in neoaccretion under low pressure and high temperature. The zircon U-Pb age of the newly obtained Chaganchulu A-type monzogranite restricts the closing time of the eastern part of the Paleo-Asian Ocean before the Middle Triassic.