In 1∶50 000 Yuanjiafangzi and three other regional geological mapping, petrology, mineralogy, geochemical and isotopic chronology were studied based on the geological characteristics of the complex rock mass in the Ulan Hill Chahar Banner, Inner Mongolia. Isotope zircon U-Pb results, ²⁰⁶ Pb / ²³⁸ U surface age (225.4±1.6) Ma, can be the Jurassic emplacement age. The rock mass distribution is controlled by the regional NE fault obviously. The rock geochemical data shows that it belongs to calc-alkaline rock series. The Donghaokan diorite may be mantle origin with the crustal material mixing. Ulan Hill granites may be crust origin. REE curves showed a rightward flat type with LREE enrichment, HREE apparently absent, and no obvious Europium anomaly exist.