The relationship between Cu—Mo—Au mineralization in Machangqing ore deposit is significant to understanding the process of ore forming and geological exploration. 40Ar/39Ar isotopic dating method is performed on two hydrothermal muscovite samples collected from skarn type Cu—Mo—Au ore in Luandongshan segment and altered rock type Au ore in Rentouqing segment. Muscovite from the skarn type (B119) ore yields the plateau age of 3525±036 Ma、the normal isochron age of 350±18 Ma and the inverse isochron age of 348±19 Ma; Muscovite from altered rock type ore (B118) yields the plateau age of 3535±032 Ma、the normal isochron age of 3444±099 Ma and the inverse isochron age of 344±12 Ma. These ages are consistent with the syenite age (356±03 Ma), granitic porphyry age (350±02 Ma) and the age of Cu—Mo mineralization(358±16 Ma), which indicates that the Machangqing Cu—Mo—Au deposit has link with the magmatic combination of syenite porphyry +monozonite porphyry +granitic porphyry +porphyritic granite and that Cu—Mo—Au mineralization is the product of the identical structural—magmatic— metallogenic system.