Abstract: In order to investigate the formation age and tectonic background of the syengranite in Ulanhot region, the authors have studied its zircon U-Pb age and geochemical characteristics. The results show that LA-ICP-MS zircon U-Pb age is (219.7±1.2)Ma, which represents its formation age. The syengranite is rich in silicon and alkali, while the content of aluminum, calcium, magnesium and iron is low. These rocks also have high rare-earth elements content, inapparent fractional distillation between light rare-earth elements and heavy rare-earth elements, and obvious negative abnormal Eu. For the trace elements, these rocks are rich in large ion lithophile elements (Rb and K) and high field strength elements( U, Th, Hf and HREE), while they are poor in Sr, Eu, Ba and Ti. The 10 000×Ga/Al value (3.53 ~ 5.09) is higher than the lower limit value (2.6) of A-type granite, and significantly higher than the average value of the I-type and S-type granites (2.10 and 2.28, respectively). Therefore, the authors concluded that Triassic syenogranite is A-type granite, and the formation environment belongs to post-orogenic lithospheric extension tectonic setting after the closure of Paleo-Asian Ocean.