The Guangxingyuan composite granites is located at the upper reaches of Xar Moron River, eastern Inner Mongolia. It is mainly composed of quartz diorite and monzonite granite in center, few gabbro and diorite at the edges. The composite granite body are characterized with SiO2(48%～71.36%)，K2O(1.4%～4.29%) contents, K2O< Na2O and A/NKC=0.81～1.1,and the calc-alkaline rocks to tholeiitic series. The REE are strongly fractionating patterns with medium negative Eu anomalies, and the HREE enrichment. The geochemical characteristics are similar to the typical island arc magma. Using High-precision SHRIMP U-Pb zircon dating method, we determine the quartz diorite and quartz monzonite diorite from the Guangxingyuan composite granite body and respectively gain the 206Pb/238U weighted mean ages which are 263.8±2.1Ma and 263.3±2.5Ma. the results indicate that the age of the magma emplacement and crystallization is Late Permian.From the comprehensive study including the regional geochronology and geochemistry data, it is suggested that there are the process from the Paleo-Asian Ocean subduction to the continental collision at 263~247Ma between the north margin of North China Plate to the south margin of Siberia Plate