Located in the north of Suizhou, syenogranite occurs in diabase as veinlike, and strikes NW—SE direction. SHRIMP UPb dating yields a weighted mean 206Pb/238U age of 648.8±1.9 Ma (MSWD=0.86) for the zircons from syenogranite, indicating that syenogranite belongs to Neoproterozoic. Lithochemical analysis shows that syenogranite is slightly metaluminous and belongs to the highK calcalkaline series. The syenogranite is characterized by high SiO2 (70.67%~75.75%), high alkali (K2O+Na2O=7.28%~8.53%), high FeOT/MgO (FeOT/MgO=26.37~35.50), low CaO (0.60%~1.53%) and MgO (0.07%~0.12%) contents. Chondritenormalized REE patterns of the syenogranite are characterized by weakly HREE depletion with Eu anomalies (δEu=0.33~0.56). The values of 1000Ga/Al and Zr+Nb+Ce+Y range from 2.60 to 3.41 and from 552.48×10-6to 648.87×10-6, respectively. The spider diagram of the trace elements shows the enrichment of largeion lithophile elements (Rb, K, Th, etc), relative enrichment of high field strength elements (Zr, Hf, Nb, Ta), relative depletion of Sr, P and Ti. All these features above suggest that syenogranite belongs to A1type granite. Combined with the regional tectonic evolution, it can be concluded that syenogranite formed in a regional extensional setting. During the Neoproterozoic, the tectonic regime in the QinlingTongbaiDabie area changed from compression to extension, under which the upwelling magma resulted in the formation of the A1type syenogranite.