Abstract: Lying along the Hegenshan collisional orogenic suture zone in Xi Ujimqin Banner of Inner Mongolia, the Shijiangshan Atype granite intruded into Early Carboniferous Diyanmiao-Baiyinbulage ophiolite as well as Early Permian Shoushangou Formation and Dashizhai Formation, and consists mainly of monzogranites. The granite is geochemically characterized by high SiO₂ (74.18%~77.16%), K₂O (4.31%~5.07%), high absolute alkali values (Na₂O+K₂O=8.44%~9.16%), low Al₂O₃, CaO, MgO, TiO₂, P₂O₅, Sr, Ba, Eu, Ti, P values, and higher Ga/Al (3.98~6.09), (Na₂O+K₂O)/CaO, K₂O/MgO, TFeO/MgO, Rb/Nb, Y/Nb, Sc/Nb ratios. It is characterized by typical flat or slight right-inclined gull-wing shaped REE distribution patterns with obvious negative Eu anomalies (δEu=0.01~0.19). The Shijiangshan monzogranite exhibits typical geochemical characteristics of A-type granite, being significantly different from I, S and M type granites in geochemistry. According to the chemical subdivision diagrams of the A-type granitoids, the Shijiangshan A-type granite belongs to aluminous A₂-type granitoid, formed and emplaced in a post-orogenic extension setting. LAICP-MS zircon U-Pb dating shows that the ages of the granite are 159.8±1.3Ma, 143.1±1.3Ma and 136.20±0.69Ma, suggesting that it was produced during Late Jurassic to Early Cretaceous and that the Hegenshan suture zone was at the post orogenic extension stage in the Late Jurassic-Early Cretaceous period.