Abstract: The geological and geochemical characteristics of Xialadi ultrabasic rock of western Qinling were studied systematically in this paper. The results show that the characterization of Xialadi ultrabasic rocks is low SiO₂, Mg rich and alkaline poor, in which metamorphic preexisting rocks belongs to the class of peridotite. The distribution of trace elements and rare earth elements (REE) among various rock types is different. The primary magma of Xialadi ultrabasic rocks originates from upper mantle, whose genetic type belongs to the mantle peridotite of subduction zone. Materials of crustal source and marine carbonate were added to Xialadi ultrabasic magma during its evolution, which resulted in the special geochemical composition characteristics of Xialadi ultramafic rocks with high Al₂O₃ and CaO. In this paper, a preliminary discussion was carried out on the reasons of the differences in geochemical characteristics of Xialadi ultrabasic rocks due to the effects of alteration.