Chifeng, Inner Mongolia, is mainly located in the Bainaimiao island arc belt of the northern margin of North China craton. This paper uses Hongmiaozi syenogranite and Jiguanshan granite porphyry to conduct related research, the results show that both of the granites are rich in SiO2 (72.77% ~ 76.80%), K2O(4.30%~5.38%), and poor in MgO(0.09% ~0.21%), CaO(0.21% ~0.56%). With the aluminum saturation index(A/CNK) is 1.09~1.29, the granites are high in Al2O3(12.49~13.54%), and the average value of 104×Ga/Al is 2.68(>2.6), it indicates that the type of Hongmiaozi syenogranite is from I-type to A-type granites, and is more close to aluminous A-type granites. The Jiguanshan granite porphyry belongs to the typical aluminous A-type granites. LA-ICP-MS zircon U-Pb ages are 392.0±2.5Ma(the syenogranite) and 377.4±1.6Ma(the granite porphyry), which reveal that the granites were formed in Late Paleozoic. There are amounts of Indosinian-Yanshanian granites in the Xing’an-Mongolian Orogenic belt, and the discovery of Late Paleozoic intrusions suggests that Xing’an-Mongolian Orogenic belt is a compound orogenic belt, and it hasmulti-phasesorogenic processes since started in the Late Paleozoic. Combining with the characteristics of regional geologic and geochemical data, the A-type granites were formed in the extensional setting after the collision between the Bainaimiao island arc and the northern margin of North China Craton. This research is significant in that it is the first time getting accurate isotopic age in the Bainaimiao island arc belt, and provides evidence for the collision between the Bainaimiao island arc belt and the North China Craton, which ended in the Early Devonian.