Objectives：The syenite porphyry is an important magmatism record of China—Mongolia border region in the period of Mesozoic Era. The formation age and geochemical characteristics of the adamellite are significant to reveal the tectonic framework and evolution history at that period. Methods: Samples were crushed into granules of less than 200 mesh and then analyzed for major and trace elements. All analyses were conducted at the IGG’s State Key Laboratory of Lithospheric Evolution in Beijing, China. Major elements were determined by xray fluorescence spectrometry on fused glass disks using an Axios mineral separation tool, with analytical uncertainties ranging from 1% to 5%. Traceelement and rareearth element concentrations were determined by ICPMS with an ELEMENT system. According to Chinese national standards GSR1 and GSR2, the error was <5% for trace elements with concentrations of 10×10-6 and <10% for trace elements with concentrations of <10×10-6. Zircon LAICPMS UPb isotope analyses were performed at the Chinese Academy of Geological Sciences using a laserablation system (193 nanometers (nm), GeoLas 200M) coupled to a Neptune (Thermo Fisher) Multicollector Inductively Coupled Plasma Mass Spectrometer (MCICPMS). Zircon U Th Pb measurements were made on 32 nm diameter spots on single grains. NIST 612 was used as an internal standard for U, Th, and Pb analyses and zircon GJ1 was used as the external calibration standard. Common lead was corrected using the method of Andersen (2002). Isotopic ratios and element concentrations were calculated using the ICPMS Data Cal software. Ages were calculated using ISOPLOT 3. Results: The granite was formed in the Middle—Late Jurassic period and the UPb age of zircon is 170.6±17 Ma. The geochemical data of granite show that it is highK calcalkaline. Also the granite is characterized with high silicon, with SiO2 (7399%～7428%), A12O3 (1236%~1430%), and MgO（017%~045%）, peraluminous. The total content of REE is 5192×10-6 to 5832×10-6. The REE distribution patterns demonstrate a significant negative Eu anomaly and a “swallowtype” shape. The spider diagrams of primitive mantle standardized trace elements show enrichment of Rb, Th, U, K, Zr, Hf, strong depletion of Ba, Sr, P, Ti and medium to slight depletion of Nb and Ta. The initial n(143Nd)/n(144Nd) values are high (0512320~0512451), and the average value is 0512404. The εNd(t) values are all negative (-46~-2.3).  Conclusions: The characters of major elements, trace elements, and isotopes show that the syenite porphyry was formed at the transitional period from syncollision to postorogenic tectonic systems, with extensional geotectonic environment. The crustal thickening and the partial melting of crustal materials are possibly main dynamic mechanism to form the granite.