Using the 40Ar_39Ar isotopic chronological method to analyze K-feldspar from moyite in the Qiaohuote copper deposit, the authors obtained a plateau age of 274.78±0.44 Ma and an isochron age of 272.7±3.0Ma. As there existed no tectonic deformation and hydrothermal alteration in themoyite intrusive body after its rock-forming stage, the 40Ar-39Ar isotopic age should represent the crystallization age of the K-feldspar in moyite, i.e. the late crystallization age of the moyite intrusive body. Based on such factors as the spatial relationship between the moyite intrusive and the Qiaohuote copper orebodies, the variations of copper ore grade, the REE characteristics of the moyite and the copper orebody, and the H and O isotopic composition of fluid inclusions in the copper ores, it is held that the ore-forming process of the Qiaohuote copper deposit was related directly to the intrusive activity of the moyite, and therefore the crystallization age of the K-feldspar in moyite should approximately represent the lower limit of the metallogenic epoch of the Qiaohuote copper deposit.