Shamai tungsten deposit is a medium sized magmatic hydrothermal deposit located in Dong Ujimqin Banner of Inner Mongolia. The ore bodies mainly occur in biotite monzonite granite and biotite monzonite granite porphyry. In this study, the petrography, LA-ICP-MS zircon U-Pb chronology and petrogeochemistry of biotite monzonite granite and biotite monzonite granite porphyry are studied in order to clarify the genesis and age of the two rocks and provide further data for regional prospecting. The results show that the LA-ICP-MS zircon U-Pb ages of biotite monzogranite are 135.6±1.6 Ma and 136.3±1.8 Ma, and the biotite monzonite granite porphyry is 138.6±1.1 Ma. The main elements show they are peraluminous high potassium calc alkaline granite which are characterized by high SiO₂ (73.73%~78.23%), Na₂O+K₂O (7.56%~8.89%)and low MgO (0.09%~0.20%), CaO (0.51%~0.89%), TiO₂ (0.03%~0.12%). They are enriched in Rb, K, Th, U, and depleted in Sr, Ba, Nb, P, Ti, with strong negative Eu anomaly and high FeO^T content, FeO^T/MgO and FeO^T/(FeO^T+MgO) ratio indicating the characteristics of A-type granite. The zircon U-Pb age of the Shamai granite is consistent with the age range of the large-scale metallogenesis in eastern China. The tectonic environment discrimination diagrams indicate that it was formed in the extensional tectonics environment after the continental collision in the Yanshanian period, which is related to the lithospheric thinning of northern margin of the North China Craton.